Scope
Reference
FA2416
Description
From January 2026, the South East Strategic Reservoir Option (SESRO) project name is changing to White Horse Reservoir, with a strapline of 'a space for nature, a place for people.'
As our reservoir proposals have evolved, so too has the potential legacy it could have. The proposed reservoir is a critical drought insurance policy for the next century and beyond - but it's also being designed as a place for people to use and enjoy for many years to come.
At this exciting stage in development, it's important that we give the project a new identity: one that better reflects the crucial role it will play in shoring up water supply, as well as the broader benefits it will deliver for future generations.
It is the same project, with the same vision, but with a new name that will help people recognise it more easily. For us, the name White Horse Reservoir roots this project in local heritage and in the natural world around us. Equally important as the project's new name, the strapline tells us more about where the project's strengths lie; a space for nature, a place for people.
To stay up to date and find out more, please visit www.thames-sro.co.uk/whitehorsereservoir
Thames Water is leading the development of the new reservoir project, in partnership with Affinity Water and Southern Water.
Thames Water is responsible for delivering the development phase, developing the commercial model for the project and for running the procurement processes to appoint the project's Main Works Contractor (MWC) and later, the appointment of an Infrastructure Provider (IP).
Thames Water is delivering the project under the Specified Infrastructure Project Regulations, or "SIPR", first established and used for the Thames Tideway Tunnel project. Under this approach a new regulated entity, known as an IP will be established to finance and deliver the project, holding a Project Licence granted by Ofwat.
Delivery under SIPR is subject to a notice to specify an infrastructure project, which is currently under development between Thames Water and Ofwat.
Following the approach taken on the Thames Tideway Tunnel project, Thames Water is separately procuring the Main Works Contract and the IP Contract.
This tender notice relates to the procurement of the Main Works Contract only, which comprises the award of a multi-supplier Framework Agreement and a single Call-Off Contract.
The Framework Agreement will be a bespoke framework agreement which is described further in the document associated with this tender notice.
The Call-Off Contract will be based on the NEC4 Engineering and Construction Contract June 2017 (with amendments January 2023) using main option C, secondary options including clause X22 (early contractor involvement ("ECI")), and bespoke amendments, which are described further in the documents associated with this tender notice.
The Call-Off Contract two-stage ECI approach comprises a design and construction planning stage ("Stage One"); and a detailed design and build stage ("Stage Two"). The two-stage ECI Call-Off Contract includes a key decision point that is based on conditions precedent that must be satisfied before a Notice to Proceed to Stage Two can be issued.
The Development Consent Order (DCO) reference design (provided by others) will inform the requirements and constraints within the Call-Off Contract scope (Scope). The MWC will develop the design for construction to comply with the Scope, which will be integrated with the discharge of certain planning requirements "secondary consents" and construction planning for Stage Two.
Tenderers will be required to submit a Target Price to deliver the Call-Off Contract requirements included in the tender documents. As part of the Call-Off Contract, the Pricing Information will set out the circumstances where the tendered Target Price can be adjusted during Stage One ("Adjustment Events"), for example, if the Client changes the Scope. Following a Notice to Proceed to Stage Two, the Target Price (established during Stage One) will be subject to amendment in accordance with the compensation events included in the Call-Off Contract.
The decision gate to proceed to Stage Two will be dependent on a number of matters, including: 1) appointment of the IP; 2) an accepted design (insofar as it has been developed in Stage One) that meets the requirements of the Call-Off Contract; 3) confirmation of the Target Price in accordance with the Pricing Information; and 4) the granting of the DCO.
At the end of Stage One, the Call-Off Contract will be novated to the IP from Thames Water. From the point of novation, the IP will become the MWC's Client and contract counterparty throughout Stage Two, administering the Call-Off Contract and making payments to the MWC accordingly.
Subject to the issue of the Notice to Proceed, Stage Two will commence with an initial period to discharge any remaining secondary consenting issues, followed by mobilisation to commence construction. Following construction, a testing and commissioning phase will be required with a target date for the reservoir to be operational from 2040 (although filling the reservoir with water could take several years). Some construction of visitor facilities, as well as landscaping activities will likely continue until 2043.
The Call-Off Contract involves the design, build, test and commission of a new reservoir with an operational capacity of 150 million cubic metres (Mm³) and water surface area of circa 6.7km2, situated to the South-West of the town of Abingdon in Oxfordshire, which will support long-term drought resilience across the South East of England.
White Horse Reservoir is a proposed fully bunded, non-impounding raw water storage reservoir in the upper catchment of the River Thames.
Water will be abstracted from the River Thames during periods when sufficient river water is available and conveyed to the reservoir via a pumping station and circa 4km of tunnels.
White Horse Reservoir is being developed in full compliance with the Reservoirs Act 1975. A Construction Engineer and Reservoir Advisory Panel have been appointed to oversee the design and construction, ensuring adherence to safety standards and regulatory requirements throughout the project lifecycle. The Construction Engineer appointment will continue through the entire construction phase, through first filling and the initial years of operation. The Reservoir Advisory Panel will provide regular review of the design and construction activities and draw upon best practice from around the world.
The reservoir embankment and associated structures will be designed to national and international standards and guidance documents.
To deliver the reservoir, watercourse diversions and replacement floodplain storage are required.
A conveyance system will be implemented to transport water to and from the River Thames, and to the interface points with the Thames to Southern Transfer (T2ST) and Farmoor Transfer projects.
The reservoir includes passive design provisions for future integration with other strategic water resource and flood alleviation schemes.
Other associated infrastructure forms part of the works, including roads, rail sidings, recreational facilities, utilities diversions, renewables and power supplies, and drainage.
The scope of the Call-Off Contract will include, but not be limited to:
· Design and construction planning.
· Mobilisation and enabling works (incl. utility diversions, site clearance and demolition, environmental and archaeological surveys, utility connections, securing the site boundary, habitat creation and species relocation, geotechnical investigations and various other activities).
· Creation of a temporary rail siding and materials handling area on the Great Western Main Line, required to facilitate the delivery of certain materials by rail freight and therefore reduce the total volume of material imported and exported by road.
· Creation of watercourse diversions, floodplain and drainage, as well as initial works relating to the future restoration of the Wilts and Berks Canal.
· Reservoir earthworks, excavation to create the borrow pit and embankments, Replacement Flood Storage, other components of the landscape scheme and road embankments.
· Tunnelling and pipelines including the reservoir tunnels and river tunnel.
· Road construction (including overbridges).
· Concrete works for the operational structures, such as the reservoir towers and pumping station.
· River Thames intake/outfall structure, requiring a sheet-piled temporary cofferdam in the River Thames.
· Construction of ancillary buildings.
· Mechanical and electrical infrastructure and fit-out.
· Building construction and fit-out.
· Landscaping.
· Land and habitat management.
Note: The total value (estimated) stated in this Tender Notice is estimated at Q2 2025 prices and therefore excludes any allowance for inflation over the life of the contract from this date.
Commercial tool
Establishes a framework
Total value (estimated)
- £5,700,000,000 excluding VAT
- £6,840,000,000 including VAT
Above the relevant threshold
Contract dates (estimated)
- 11 August 2027 to 31 March 2043
- 15 years, 7 months, 21 days
Main procurement category
Works
CPV classifications
- 09330000 - Solar energy
- 43123000 - Tunnelling machinery
- 45111100 - Demolition work
- 45111200 - Site preparation and clearance work
- 45112400 - Excavating work
- 45112450 - Excavation work at archaeological sites
- 45112500 - Earthmoving work
- 45112700 - Landscaping work
- 45212100 - Construction work of leisure facilities
- 45212423 - Cafeteria construction work
- 45212600 - Pavilion construction work
- 45221240 - Construction work for tunnels
- 45221247 - Tunnelling works
- 45231110 - Pipelaying construction work
- 45231300 - Construction work for water and sewage pipelines
- 45231400 - Construction work for electricity power lines
- 45232100 - Ancillary works for water pipelines
- 45232152 - Pumping station construction work
- 45232153 - Construction work for water towers
- 45233120 - Road construction works
- 45233226 - Access road construction work
- 45233227 - Slip road construction work
- 45234100 - Railway construction works
- 45246400 - Flood-prevention works
- 45247100 - Construction work for waterways
- 45247110 - Canal construction
- 45247120 - Waterways except canals
- 45247200 - Construction work for dams and similar fixed structures
- 45247210 - Dam construction work
- 45247211 - Dam wall construction work
- 45247270 - Reservoir construction works
- 71221000 - Architectural services for buildings
- 71240000 - Architectural, engineering and planning services
- 71311100 - Civil engineering support services
- 71311220 - Highways engineering services
- 71311230 - Railway engineering services
- 71312000 - Structural engineering consultancy services
- 71313000 - Environmental engineering consultancy services
- 71322200 - Pipeline-design services
- 71322400 - Dam-design services
- 71510000 - Site-investigation services
- 71520000 - Construction supervision services
- 71540000 - Construction management services
- 71630000 - Technical inspection and testing services
- 90712400 - Natural resources management or conservation strategy planning services
Contract locations
- UKJ14 - Oxfordshire
Framework
Maximum number of suppliers
Unlimited
Maximum percentage fee charged to suppliers
0%
Framework operation description
A single Call-Off Contract will be awarded immediately following the establishment of the multi-supplier Framework Agreement. The Call-Off Contract will be awarded to the most advantageous tender identified at the end of either the ITT Stage or, if used, at the end of the BAFO Stage, in accordance with the criteria set out in the ITT.
Other than the Call-Off Contract, there will be no guarantee of any other services or works being awarded under the Framework Agreement. However, if circumstances arise where the Call-Off Contract is unable to proceed beyond specified decision points within ECI Stage One or beyond ECI Stage One, then the contracting authority may, at its sole discretion, (i) directly award a new Call-Off Contract to a different framework contractor or (ii) undertake a mini competition, as explained briefly below.
If the contracting authority elects to directly award a new Call-Off Contract under the Framework Agreement, then the procedure will be to award to the next highest ranked framework contractor, i.e., the 2nd placed framework contractor, using the rankings established at the conclusion of the ITT stage or, where applicable, the BAFO stage, and included in the Framework Agreement. Any new Call-Off Contract award will be contingent on the 2nd placed framework contractor confirming the availability of key persons (or suitable replacements) and updating their originally tendered Target Price to account for any Adjustment Events that have occurred during Stage One. If the contracting authority is unable to reach agreement with the 2nd placed framework contractor, then the contracting authority may approach the 3rd placed framework contractor and so on.
If the contracting authority chooses to undertake a mini competition, the most advantageous tenderer out of the framework contractors eligible to participate in the mini competition will be awarded the replacement Call-Off Contract.
Award method when using the framework
Either with or without competition
Contracting authorities that may use the framework
Establishing party only
Participation
Legal and financial capacity conditions of participation
As set out in the PSQ Pack (sections 4.4 - 4.5 of Part 1 and sections 4.1 - 4.2 of Part 2)
Technical ability conditions of participation
As set out in the PSQ Pack (sections 4.5 - 4.6 of Part 1 and sections 4.2 - 4.3 of Part 2)
Submission
Enquiry deadline
7 April 2026, 11:00am
Submission type
Requests to participate
Deadline for requests to participate
24 April 2026, 11:00am
Submission address and any special instructions
https://www.smartsurvey.co.uk/s/WHR_MWC_APP_BRF_REG/
This link will take interested parties to the Applicant Registration Form. Completing the Applicant Registration Form will then, subject to confirmation, provide suppliers with access to the secure site containing the Procurement Specific Questionnaire Pack (PSQ Pack) and submission portal.
Tenders may be submitted electronically
Yes
Languages that may be used for submission
English
Suppliers to be invited to tender
Maximum 4 suppliers
Selection criteria:
The contracting authority will assess PSQ Responses in accordance with the Assessment Methodology published in the PSQ Pack to identify eligible Applicants that have met the Minimum Standards and to shortlist the four highest scoring Applicants. It is intended that the top four Applicants will be invited to Tender, however, the actual number of Applicants invited to Tender could be more or fewer than four depending on whether the scenario arises that is set out in PSQ Pack Part 1, paragraphs 4.6.23 and 4.6.24 of the PSQ Pack.
Award decision date (estimated)
13 July 2027
Award criteria
| Name | Description | Type | Weighting |
|---|---|---|---|
| Technical | Summary technical award criteria: · Stage One Delivery Proposals. Sub-criteria will include: programme, resources, design development, construction planning, and delivery of innovation and... |
Quality | 70% |
| Commercial | Summary commercial award criteria: · Tendered Total of the Prices. Weighting range: 26%-28%. · Fee Percentage (noting that a minimum Fee percentage constraint will be applied to discourage... |
Price | 30% |
Other information
Applicable trade agreements
- Government Procurement Agreement (GPA)
- Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP)
Conflicts assessment prepared/revised
Yes
Procedure
Procedure type
Competitive flexible procedure
Special regime
Utilities
Competitive flexible procedure description
This tender notice is for the award of a public contract - a multi-supplier framework agreement ("Framework Agreement") and an associated single call-off contract ("Call-Off Contract") - via a competitive flexible procedure in accordance with section 20(1) and 20(2)(b) of the Procurement Act 2023 ("PA23").
Request to Participate Stage:
This tender notice invites submission of requests to participate from Applicants. Having reviewed the tender notice and the associated documents, all Applicants wishing to participate in the competition for a Main Works Contract for White Horse Reservoir must demonstrate in their submissions that they meet the Conditions of Participation and all other requirements set out in the Procurement Specific Questionnaire Pack (PSQ Pack).
The PSQ Pack includes a summary of the proposed:
· Award criteria
· Call-Off Contract Scope, and
· Framework Agreement and Call-Off Contract terms and conditions
An online Applicant Briefing will be held on 11 February 2026 regarding the Request to Participate stage and the Main Works Contract opportunity. The briefing will provide an overview of the requirements set out in the PSQ Pack. Applicants wishing to attend the briefing must register using the contact details in the PSQ Pack Part 1 (section 1.2.4), by 12 noon on 10 February 2026. Registration requests will be subject to confirmation, following which confirmed attendees will be issued with joining instructions. A recording of the briefing will be made available on the contracting authority's e-Tendering System by 13 February 2026.
Requests to participate must be submitted via the contracting authority's e-Tendering system as set out in the PSQ Pack - Part 1 (Instructions for Applicants).
The contracting authority will assess each Applicant's submission in three stages as follows.
In stage 1, compliance and eligibility checks will be undertaken on a pass/fail basis; in stage 2, there will be an assessment of legal, financial capacity and technical ability to perform the contract on a pass/fail basis; and for those submissions that pass stages 1 and 2, there will be a scored technical ability assessment (stage 3) that will include a minimum score threshold and result in an overall score for each Applicant. Each Applicant's overall score will be used to determine which Applicants will be shortlisted to participate in the next stage of the procurement process.
Scored submissions will be ranked from highest to lowest and, subject to the procedure set out in the PSQ Pack Part 1 (paragraphs 4.6.20 and 4.6.21), the contracting authority intends to invite to tender the four (4) highest scoring Applicants (the shortlisted Applicants will then become the Tenderers).
The contracting authority intends to rely on section 24 of PA23 to refine the summary award criteria (as set out in the PSQ Pack) prior to inviting Tenderers to submit tenders to be assessed under section 19 of PA23 (award following competitive tendering procedure).
Invitation to Tender (ITT) Stage:
The contracting authority will share with the Tenderers an Invitation to Tender (ITT). The ITT will include the detailed award criteria (including sub-criteria); the Framework Agreement and Call-Off Contract scope; and the draft Framework Agreement and Call-Off Contract terms and conditions.
During the Tender period, there will be an opportunity for Tenderers to request necessary amendments to the published Framework Agreement and Call-Off Contract. The contracting authority will consider any requested amendments and following dialogue with Tenderers, will issue an updated Framework Agreement and Call-Off Contract (the same version for all Tenderers) that will form the basis of tendering.
Tender submissions will be evaluated in accordance with the award criteria set out in the ITT.
Following the evaluation, the contracting authority reserves the right at its discretion to award the Framework Agreement and Call-Off Contract on the basis of the Most Advantageous Tender without any negotiation.
Negotiation Stage (optional at Thames Water's discretion):
The contracting authority may engage in negotiations with Tenderers on the relevant terms of the Framework Agreement and/or Call-Off Contract. Further details in connection with the optional negotiation stage are set out in section 1.2 of the PSQ Pack Part 1 and will be confirmed in the ITT. Tenderers must not rely upon a negotiation stage being undertaken.
Best and Final Offer Stage (optional at Thames Water's discretion):
At TWUL's discretion, there may be a requirement for best and final offers ("BAFO") to be submitted. Tenderers must not rely upon a BAFO stage being undertaken.
Contract Award:
At the end of either the ITT Stage or, if used, at the end of the BAFO Stage, all Tenderers that submit a compliant tender which adheres to the relevant minimum standards set out in the ITT will be awarded a place on the Framework Agreement.
A single Call-Off Contract will be awarded following the establishment of the Framework Agreement. The Call-Off Contract will be awarded under the Framework Agreement to the Tenderer that has submitted the most advantageous tender identified at the end of either the ITT Stage or, if used, at the end of the BAFO Stage, in accordance with the award criteria set out in the ITT.
Documents
Associated tender documents
https://www.smartsurvey.co.uk/s/WHR_MWC_APP_BRF_REG/
This link will take interested parties to the Applicant Registration Form. Completing the Applicant Registration Form will then, subject to confirmation, provide suppliers with access to the secure site containing the Procurement Specific Questionnaire Pack (PSQ Pack) and submission portal.
Documents to be provided after the tender notice
The ITT will be issued to shortlisted tenderers on Thames Water's e-Tendering System
Contracting authority
THAMES WATER UTILITIES LIMITED
- Companies House: 02366661
- Public Procurement Organisation Number: PNQQ-4647-DTCV
Clearwater Court
Reading
RG1 8DB
United Kingdom
Email: SRO.procurement@thameswater.co.uk
Website: https://www.thameswater.co.uk/
Region: UKJ11 - Berkshire
Organisation type: Private utility