(BBC NEWS) — A man who is critically ill after being exposed to an unknown substance in Wiltshire is a Russian national convicted of spying for Britain, the BBC understands.

Sergei Skripal, who is 66, was granted refuge in the UK following a “spy swap” between the US and Russia in 2010.

Police declared a major incident on Sunday after he and a woman became ill at a shopping centre in Salisbury.

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