These dramatic images show how floods could devastate major cities across Britain leaving thousands of homes underwater if no flood defences were put in place.The centres of London, Birmingham, Cardiff and Liverpool would be completely submerged with properties wrecked and businesses shutdown in the event of major flooding.

Extraordinary photographs of the devastation flooding could cause were released by the Environment Agency today to warn of the dangers of natural disasters .

Major rehearsals for a possible disaster are to begin involving 10,000 people as Government tests how they, the emergency services and communities will respond. £1.8million is being spent on the test exercises which will involve ten government departments and utility companies in what ministers say is the 'largest civil defence exercise ever' in Britain.

Over the next week Exercise Watermark will test how agencies deal with flash flooding, overflowing rivers, a reservoir threatening to burst and even a North Sea tidal surge in different parts of the country. The 'dry runs' were recommended by Sir Michael Pitt when he carried out an official review into flooding in 2007 which hit parts of Yorkshire, the Midlands and the West Country.

Ministers will take part in mock emergency Cobra meetings and 'local resilience forums', which include police, fire and rescue services, local authorities and public bodies, will test their response to a potential disaster. [ DAILY MAIL UK ]