SESRO

Overview: 

South East Strategic Reservoir Option (SESRO) is a proposed new reservoir near Abingdon in Oxfordshire, being developed by Thames Water with Ardent and other partners to secure long-term water supplies. 

The reservoir will be filled over a two-year period drawing water from the River Thames. Once operational, water will be drawn to and from the reservoir as required during periods of drought and rainfall, respectively. 

 When river levels drop, or demand for water increases, water would be released from the reservoir back into the river for re-abstraction downstream. 

The reservoir would supply water to local customers as well as homes and businesses across London and the South East. It would provide opportunities to create new habitats and increase biodiversity, as well as new leisure and recreation facilities. 

Thames Water intends to submit a Development Consent Order (DCO) application to the Planning Inspectorate in 2026, seeking the powers and planning application required to deliver this nationally important infrastructure project. 

 

Background:  

Thames Water is a private utility company responsible for water supply and wastewater treatment in most of Greater London and surrounding areas. It serves approximately 9 million customers with drinking water and 14 million with wastewater services, supplying around 2.6 billion litres of drinking water daily and treating over 4 billion litres of sewage. 

Established in 1989, Thames Water is the largest of the ten regulated water and sewerage companies in England and Wales, by both customers and revenue, and therefore plays a crucial role in managing water resources in the UK. 

 

Approach:  

The South East Strategic Reservoir Option (SESRO) is a Development Consent Order (DCO) project currently in the pre-application phase.  

Since being appointed to the project in July 2024, Ardent has identified all landowners who may be affected by the 5,500-acres scheme, largely through Land Registry and contact land referencing information. Our work has involved extensive landholder engagement and outreach, in writing and in person, to build relationships, explain what the scheme will entail and the explore the prospect of acquiring land for the project. 

Meaningful engagement and negotiations with landowners will continue up to and after November 2026 when the application will be submitted. 

Since Ardent’s appointment, the red line boundary has expanded significantly due to a shallower embankment design, which requires a larger geographical footprint. This change, along with the need to meet enhanced environmental and ecological requirements, has highlighted Ardent’s adaptability and diligence in responding to evolving project parameters. 

Around 90 acquisitions are expected within the reservoir’s original proposed footprint, with Ardent anticipating at least the same number again for the additional land encompassed by the expanded outer boundary. 

Ardent will seek to negotiate wherever possible, but anticipates that compulsory purchase powers may be required in some instances, given the scale and complexity of the project.  Shortly after appointment, Ardent successfully secured two key parcels of land not previously owned by Thames Water, which has been integral to the progress of the project. 

Ardent brings the experience and expertise needed to support Thames Water in progressing this much-needed project, which has previously faced environmental and needs case objections. As the statutory consultation phase advances, engagement activity will intensify to proactively address and mitigate any concerns raised by local landowners and stakeholders.  

Private survey licence agreements have been secured with Landlords connected to an objector group, highlighting Ardent’s ability to engage, communicate and negotiate responsibly and efficiently. 

 

Benefits:  

Designed to store 150 million cubic metres, SESRO will help to counter a shortfall of over 1 billion litres of water every day for Thames Water customers in the next 50 years. It will boost resilience, support regional transfers and deliver environmental and community benefits. 

In addition to providing a secure water supply to homes in the region, SESRO will create a country park with cycle paths, walkways and a range of watersports. It will serve as an environmentally-responsible community facility as much as a water reserve. 

 

Next steps:  

The project entered a statutory consultation period at the end of October 2025. This consultation is expected to last until mid-January 2026. During this timeframe, any member of the public will be able to submit a formal consultation response. 

Ardent will support Thames Water to process feedback received and make relevant design implementation changes. A final design is expected to be agreed in May 2026 ahead of application submission later in the year. 

Ardent will support Thames Water in preparing a comprehensive suite of DCO documentation, detailing all engagement with interested parties and the offers made, which will subsequently undergo legal review. 

A final decision by the Secretary of State is expected early in 2028. Construction would likely start early in 2029 against a public operational target date of 2040.