Up to 350,000 people were warned last night they face being without fresh water for up to two weeks after the worst floods in recent UK history showed no sign of abating.

Severn Trent Water said it had set up 400 bowsers, or mini water tankers, in locations in Cheltenham, Gloucester and Tewkesbury and was handing out a million bottles of water to residents.

Emergency supplies were being put in place as the Environment Agency said water levels across central and western England were not expected to peak for another 24 to 36 hours. Experts warned the worst was yet to come in some areas. At their height, some rivers will be more than 20ft higher than normal.

The areas hit hardest were Worcestershire, Warwickshire, Herefordshire, Gloucestershire, Lincolnshire, Oxfordshire and Berkshire.

The biggest peacetime rescue operation since the Second World War, which involved thousands of people being evacuated as their homes filled with water, was being run from Scotland by the RAF Rescue and Co-ordination Centre at Kinloss in Moray.

The unprecedented rainfall on Friday - the equivalent of a month's rain in an hour - left many thousands of people without clean water or electricity.

Last night tens of thousands of people in Gloucestershire - the worst affected area - were expected to be left without drinking water as the Severn and Thames rivers threatened to overflow.

However, there was some good news for authorities last night as waters appeared to peak below the level that could have flooded a power station serving half a million homes in Gloucestershire.

The Environment Agency (EA) said the River Severn at Gloucester had reached a peak two inches below the main quay wall which protected the city centre and Walham substation.

Earlier, the agency said water levels on both rivers had exceeded those of devastating floods 60 years ago, when millions of pounds worth of damage was caused in the south of England, the Midlands, East Anglia and North Yorkshire when many rivers burst their banks.

"We have not seen flood levels of this magnitude before," Anthony Perry, an Environment Agency spokesman, said.

"This is an extreme flood event. The 1947 event on the Severn has always been the benchmark, and this has exceeded it."

Facilities at the UK's nuclear warhead Atomic Weapons Establishment's (AWE) sites in Aldermaston and Burghfield, near Reading, were also affected by the heavy rains.

A sewage plant flooded on one of the sites but tests carried out on flood water for potential radiation discovered no contamination on either site.

As the situation showed no signs of receding, with further rain forecast for the flood-affected areas today and later in the week, Prime Minister Gordon Brown promised a review.

After flying by helicopter yesterday over Gloucestershire he said the review would look at drainage and flood defences, while extra funding would help pay for essential emergency work in the aftermath of the crisis.

Repeating the government's pledge to increase spending on flood defences from £600m to £800m, he said: "Like every advanced industrialised country, we are coming to terms with the issues surrounding climate change. We are going to have to look at drainage, surface water, as well as river water, and what we are going to be able to do in the future."

His comments came ahead of government plans to build millions more homes to tackle the housing shortage and ease pressure on first-time buyers.

But the Green Paper has already been criticised for failing to rule out further construction on flood plains.

Environment Secretary Hilary Benn defended the government against claims they failed to react to the Met Office's dire weather warnings and said nothing could have guarded against the rainfall.

But Liberal Democrat leader Sir Menzies Campbell said a lack of preparation had caused a "summer of suffering" for millions of people.