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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Bodies are being buried in backyards and overwhelming morgues as officials try to find another plot of land to lay them to rest.
Authorities have warned that the death toll is likely to rise as much of the building is yet to be searched.
The PM will sound out the possibility of new free trade agreements with Gulf states for once the UK has left the EU.