The South East Strategic Reservoir Option (SESRO) has reached a key milestone with the publication of RAPID’s (Regulators’ Alliance for Progressing Infrastructure Development) draft decision proposing the scheme’s progression to gate four of its development process. The move signals that the project has achieved an advanced stage of technical and planning readiness.
Gate four approval would release £100 million to continue detailed design, environmental assessments and enabling works required before a Development Consent Order application, expected in late 2026. The funding is critical to maintaining the programme timeline, which aims for the scheme to be construction-ready by 2029 and operational from 2040.
SESRO, being developed by Thames Water, Southern Water and Affinity Water, is designed to provide 271 million litres of water per day, contributing significantly to closing a projected two-billion-litre-per-day shortfall in the South East by 2055. The proposed reservoir near Abingdon in Oxfordshire would store high-flow water from the River Thames for use during dry periods or heightened demand, supporting up to 15 million customers.
RAPID’s assessment found that the £65.44 million invested during gate three was efficiently spent and supported by strong evidence in areas including programme management, risk analysis and procurement planning. Gate four funding would enable the completion of the Preliminary Environmental Information Report and further work on flood mitigation and drainage design.
The draft decision also outlines priority actions for the scheme’s sponsors. These include updating best-value assessments through the statutory water resources planning process by June 2026, following revised capital expenditure estimates of £5.5–7.5 billion.
The consultation on RAPID’s draft decision is open until 29 January 2026, forming part of wider national efforts to address the expected five-billion-litre-per-day drinking water deficit forecast for mid-century across England and Wales.
