The Environment Agency has issued more than 20 flood alerts for north England, the Midlands, the South East and Wales as heavy rain is set to lash the country.
The Met Office has also issued a number of severe weather warnings, for the Central, Tayside and Fife, London and the South East, south-west Scotland, Lothian Borders, the South West, Strathclyde and Wales.
It warned that heavy rain of up to 30mm (1.2in) will fall over high ground in Scotland during the morning, with thunderstorms and gusts of up to 60mph along the south coast of England.
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The PM promises to double to 200,000 the number of homes built under an existing scheme aimed at easing Britain's housing shortage.
The Met Office has weather warnings in place for snow and ice until 10am in the north and west.
The plan, which would effectively strip banks of the benefit of recent corporation tax cuts, forms part of the party's election manifesto.