Thames Water has revised the design of its planned White Horse reservoir near Abingdon, Oxfordshire, and opened a new public consultation as it seeks regulatory approval amid warnings from campaigners of "catastrophic consequences". The above-ground reservoir, previously known as the South East Strategic Reservoir Option, would hold 150 billion litres of water and cover an area almost the size of Gatwick airport, forming part of the utility's plan to secure supplies for the south-east as population growth and climate change strain water resources.

The site has more than tripled in scale to 38 sq km to accommodate construction works, relocated solar farms and diverted rivers, pushing the estimated cost from £2.2bn to between £5.5bn and £7.5bn, though critics say inflation makes £7.5bn-£10bn more realistic. The reservoir would require walls up to 25 metres high, making it the largest "fully bounded" reservoir in Europe, with costs to be recovered from Thames Water, Affinity Water and Southern Water customers over the next century. Local councils have rejected the plans over flood-risk concerns, while campaign groups accuse Thames Water of underestimating costs, and the scheme's progress is complicated by the heavily indebted utility's uncertain financial future, including the possibility of special administration.