A campaign group says an independent review it helped fund raises serious doubts over the case for a giant reservoir between Wantage and Abingdon.

The Group Against Reservoir Development (Gard) commissioned an expert on water resources to bring Thames Water's latest report under the spotlight.

The company's 900-page Water Resources Management Plan (WRMP) published in May, predicts water will start running short in six years' time, unless water-saving schemes are put in place alongside the £1bn reservoir, planned for 2021.

But in a 60-page analysis, retired professor Chris Binnie claims Thames Water has not adequately justified the need. He said its arguments and figures had serious limitations resulting in conclusions which were not "robust".

Gard chairman Nick Thompson said: "It's a damning report which shows there are much cheaper alternatives to a reservoir which can be got much quicker."

He said viable alternatives suggested by Prof Binnie included transferring water from the River Severn.

A spokesman for Thames Water said it welcomed all contributions to its consultation, but did not believe transferring water from the Severn was the best option, adding: "We would urge people to view the plan in full."

The deadline for feedback on the scheme is August 27.