Prime Minister Cameron held an emergency meeting on the floods trigged by heavy rains which he said has created an unprecedented effect.
After chairing a conference call of the COBRA emergency committee on the floods, he said the situation for many was "incredibly serious".
"The level of the rivers plus the level of rainfall has created an unprecedented effect, and so some very serious flooding. We will do everything we can to help people in their hour of need," said Cameron, who is expected to visit some of the flood-affected areas tomorrow.
"More troops are being deployed as part of a plan to do whatever is needed," Cameron wrote on Twitter.
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Lancashire in northwest England and Yorkshire in the northeast were the worst affected.
Emergency teams are working to evacuate people from homes in the city of York.
The Met Office national weather service issued "red warning", which calls people in affected areas to take action.
Police advised between 300 and 400 people to evacuate near the River Ouse and River Foss in York, with up to 3,500 properties at risk.
Around 10,000 homes in the region were without electricity after a substation was damaged.
UK environment minister Liz Truss said the government will review flood defences.
She warned some rivers had not yet reached their expected high peak, saying the Army had been deployed in York, Leeds, and parts of Lancashire.