A school will be evacuated, helicopters scrambled and people rescued from rooftops this week as part of a £1.8 million exercise to test how prepared England and Wales are for devastating floods.
Exercise Watermark will involve around 10,000 people, 10 government departments, emergency services, utility companies and communities in what ministers say is the "largest civil defence exercise ever" in Britain.
By testing responses to flooding, the exercise fulfils one of the recommendations of the official review by Sir Michael Pitt into the 2007 floods which devastated parts of Yorkshire, the Midlands and the West Country.
Over the next week Exercise Watermark will test how Government, local authorities, emergency services and communities deal with flash flooding, overflowing rivers, a reservoir threatening to burst and even a North Sea tidal surge in different parts of the 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.
Five water companies and nearly all electricity providers will also be checking they are prepared for flooding.
In Lincolnshire, Sutton on Sea residents and a primary school will be evacuated and at Tattershall Country Park people will be rescued from roof tops, submerged vehicles and caravans using boats and helicopters.
Even Prince William could be involved as RAF helicopters are used as part of live water rescues, including saving people from the top of a submerged bus, at Bala Lake, in Wales.
Environment Minister Richard Benyon said: "More extreme weather and rising sea levels mean we have to be prepared to deal with the impact of a major flood.
"Exercise Watermark will be Britain's biggest ever emergency exercise and provide a unique opportunity for us to test our responses."
