Regulators have confirmed that plans for the proposed White Horse Reservoir, in the Upper Thames catchment, have reached a detailed stage of development and will receive further funding to progress towards planning permission.

The Regulators’ Alliance for Progressing Infrastructure Development (Rapid), the joint body formed by Ofwat, the Environment Agency and the Drinking Water Inspectorate, said the White Horse project, previously known as South East Strategic Reservoir Option (Sesro), has completed gate three of its multi-stage gated process. Rapid has approved an allowance of £298M to support work up to the next stage, known as gate four.

That funding will be used to carry the project through to a Development Consent Order (DCO) application, which developers expect to submit in November this year.

The reservoir is being developed as a partnership between Thames Water, Southern Water and Affinity Water. The scheme, located south-west of Abingdon, Oxfordshire, will see the construction of a reservoir with a capacity of 150Mm³, equivalent to as much as 271Ml per day.

Rapid had recommended the proposed reservoir should progress to the next stage of development after finding the project sufficiently mature to warrant further public money late last year.

Rapid said the new reservoir is important in the context of an anticipated regional supply shortfall. The regulator has cited a forecast deficit of more than 2bnl per day in the south-east of England by 2055 if additional supply measures are not delivered.

The White Horse Reservoir is one of several strategic options being considered alongside demand-side measures such as leakage reduction and improved water efficiency.

It is currently envisaged the project will move to construction in 2029 and then become operational around 2040, with the reservoir intended to start addressing supply–demand pressures from the early 2040s.

Rapid’s gate-three confirmation is significant because it indicates the scheme has reached a detailed level of development, but the alliance also set out a number of “priority actions” that the project partners must address. These relate to biodiversity net gain, archaeological and historical impacts, and the need to update best-value assessments through the statutory Water Resources Management Plan (WRMP) process.

Rapid emphasised that whether White Horse remains the best value option will be determined in the WRMP process, not through Rapid’s gated review.

Each priority action has a specified deadline and will be monitored through regulator checkpoint meetings, Rapid said.

The project will continue to be assessed under the current Rapid process until it completes gate four and Ofwat’s Major Projects stage three, after which it will transition into the newly launched Major Water Infrastructure Programme (MWIP). The MWIP, introduced this year, combines Rapid and Ofwat decision stages into a single framework with gates running from A to F that cover a scheme’s whole lifecycle from inception to operation.

The White Horse proposal will now move into more detailed planning and environmental work ahead of the DCO application.

Earlier this year, Thames Water fired the starting gun on the “extensive” process for appointing a main contractor to design, build, test and commission its major new Oxfordshire reservoir in a deal worth £5.7bn.

In the summer of last year, Thames Water said the reservoir is expected to cost between £5.5bn and £7.5bn, triple its previous estimate, after doing more detailed design work.

Rapid managing director Paul Hickey said: “The South East of England faces a projected water shortfall of more than 2bnl a day by 2055.

“The White Horse Reservoir is a major part of the plan for addressing this gap, providing resilient water supplies for up to 15M customers across London and the South East.

“This next step will allow the companies to complete the essential preparatory work needed to keep this scheme on track to be construction ready by 2029. We will continue to apply rigorous scrutiny at every stage to make sure this project delivers for customers, local communities and the environment.”

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