Supporters of the far-right British National Party and English Defence League have erected gallows outside the Old Bailey as part of a protest demanding capital punishment for the men who murdered Fusilier Lee Rigby.
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Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.