The Prime Minister's spokesman has reiterated the "specific threat" to Westeners in Benghazi., but would not say what that was, or whether linked to Mali and Algeria.
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Police found one child chained to the ground, another tied to a door with a dog lead, while six others were also rescued.
Wintry scenes across the UK this late in April have not been seen since the mid-1980s.
The Labour leader will also announce an inquiry into anti-semitism and other forms of racism to be chaired by Shami Chakrabarti.