Thousands of people are to take part in a "mass sleep out" this evening to protest against the government's so-called 'bedroom tax' and other welfare changes.
The Government's withdrawal of housing benefit from social tenants with spare rooms - officially described as a "spare room subsidy" - is described as a "bedroom tax" by critics.
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The country's counter-terrorism forces have regained control of the facility.
The commissioner of the Metropolitan Police has said he cannot promise the public an attack will not take place.
The showers are likely to be particularly heavy across northern parts of the country.