Holding back the floodwater
The Environment Agency is warning that London would be completely submerged if no flood defences were in place - with Canary Wharf completely under water.
Images were released of a drowned East End as rehearsals for a disaster got underway this week.
Named Exercise Watermark the UK's biggest ever civil protection agency exercise will test how the authorities would respond.
Environment Agency chairman, Lord Chris Smith, said: "Exercise Watermark will test the plans that Government, the Environment Agency, local authorities and communities have put in place since the devastating floods of 2007. It will help protect lives and homes against future floods."
Some of the planned exercises include evacuating schools and installing flood defence barriers designed to protect properties, live floodwater rescues by the RAF from rooftops and submerged vehicles, and a variety of flood awareness raising activities.
Defra has also announced grants worth £820,000 to emergency services, charities and other groups to pay for flood rescue equipment and training. The grants are part of a £2m fund to improve flood response in England and Wales. All the equipment bought with the funding will be added to the National Asset Register of flood rescue resources that can be called upon in the event of a major flood.
For more information go to environment-agency.gov.uk or call 08459 881188.