Prime Minister Gordon Brown has visited some of the areas hit by floods as hundreds of homes are evacuated in Oxford.Tributaries of the River Thames spilled over into its historic streets, forcing police to evacuate 250 homes in the Osney area. Reading and Henley are still at risk, although the Osney Mead substation is no longer under threat.An Environment Agency spokesman said: "There are six severe flood warnings in place. It looks as if we are going to get up to 20 millimetres of rain across the board tomorrow. That won't cause devastation but will not help clean-up efforts."Elsewhere, up to 340,000 people in Gloucestershire could be without fresh water for a fortnight despite floodwater receding along the River Severn.Emergency services have managed to restore electricity to more than 48,000 houses, but Severn Trent said mains water supplies could be off for two weeks.In Cheltenham, Gloucester and Tewkesbury - where water levels have fallen by over six inches - the company has set up 500 bowsers, with a fleet of tankers re-filling them round the clock. Three million litres of drinking water will be provided, it said.As the River Thames continues to rise, residents in the Botley Road vicinity of Osney, as well as East Street, West Street, South Street, Bridge Street, Riverside Road and Earl Street were urged to seek shelter at Oxford United's Kassam Stadium.River levels remain high in Abingdon and there is the threat of severe flooding from Eynsham Lock, Eynsham, to Sandford Lock, Sandford-on-Thames, and from there down to Days Lock on the Thames.Levels are expected to peak in Wallingford and flooding is predicted to start in Henley on Wednesday afternoon with Pangbourne, Purley and Mapledurham braced for a peak during the evening while flooding is expected to start later tonight in Reading and Caversham.The flood peak is forecast to reach Marlow, Cookham, Datchet, Wraysbury, Staines, Laleham and Shepperton later in the week but with only limited flooding.And the towns of Windsor, Eton and Maidenhead will be protected from the flood waters by the Jubilee and Cookham flood defences, the EA said.Eddie Murphy of Oxfordshire Fire and Rescue said plans are in place to maintain electricity supplies to "essential users" such as the John Radcliffe Hospital.Mr Murphy said: "Osney Mead substation is likely to be affected in the early hours of this morning. It's likely that domestic users will be affected by a power cut today."Mr Murphy said the brigade was in the process of evacuating people living in two streets near the Botley Road area of the city.The insurance bill for floods in June and July could hit £3 billion. Farmers have said flooded areas are making milk collections from dairy farms impossible while the harvesting of barley and rapeseed has been brought to a halt in many regions.Additionally, potato and salad vegetable crops have been badly damaged and livestock losses have been heavy in some regions with the National Farmers Union reporting more than 1,100 sheep lost in just three farms in central England.The Government has pledged a further £10 million to help battle the floods - in addition to the £14 million initially promised by Prime Minister Gordon Brown earlier this month.Environment Secretary Hillary Benn said the recent crisis - the worst flooding for more than 60 years - is far from over and has caused "considerable human distress".The Queen has added her support, saying she is "shocked and deeply concerned" by the devastation.Meanwhile, the Red Cross has launched a nationwide appeal to raise money to help tackle the effects of the flooding, which raised £300,000 in the first hour.© Independent Television News Limited 2007. All rights reserved.