Britain was engaged in a diplomatic row with the United States last night over the fate of two Londoners suspected of being members of the murderous Islamic State cell dubbed “the Beatles”.

James Mattis, the US defence secretary, has ruled out sending Alexanda Kotey and El Shafee Elsheikh to Guantanamo Bay, the US internment facility in Cuba, after they were captured in Syria, officials have said. He appears to favour putting foreign Isis fighters on trial in their country of origin.

It is understood that Gavin Williamson, the defence secretary, does not want the men to return to Britain to face trial. Kotey, 34, and Elsheikh, 29, were stripped of their British citizenship after joining Isis. “The day these barbaric terrorists turned their back on