George Osborne has said Moody's message is "explicit" to carry on with austerity.
He says "we can either abandon our efforts to deal with debts" or we can "redouble our efforts" and make a brighter future for our children.
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Cloudy and damp across much of England and Wales, although the rain should turn lighter and more patchy by the afternoon.
A British journalist based in Egypt has been expelled from the country as authorities tighten control over the media ahead.