Anti-terror police are searching a house in Crawley, West Sussex, amid claims that a Briton staged a suicide bomb attack on a prison in Syria, last week.
He is believed to be 41-year-old Abdul Waheed Majeed, ITV News understands.
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No one has immediately claimed responsibility for the attack.
Met Office says it is set to be “a glorious day” in most areas
He had been in the US to attend the Def Con hacking convention.