With virtually all the votes counted, NBC News declares Mitt Romney the apparent winner in North Carolina. #NBCPolitics
The state was an outside hope for Obama's team.
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The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.
Prime Minister Theresa May announced the decision from Downing Street.
A man, apparently armed with a small axe and a large stick, was detained close to the event and police cleared the area as a precaution.