The announcement brings to 26 the total number of people suspected of involvement in Mahmoud al-Mabhouh's assassination, which is widely believed to have been the work of Israel's secret service, the Mossad. 

The six new British names are Mark Daniel Sklar, Roy Allan Cannon, Daniel Marc Schnur, Philip Carr, Stephen Keith Drake and Gabriella Barney. A Foreign Office spokesman said the government believed their passport details had been used fraudulently.

"We can confirm that six more U.K. passports have been identified. We will seek to make contact with these individuals and offer consular assistance as we have the previous individuals. We continue to work closely with the Emirati authorities. The foreign secretary and others have made clear we expect full Israeli co-operation."

It was not immediately clear where the six live.

The mother of Sklar, who declined to give her name, said her son lived and worked in Israel. She said neither she nor her son had been contacted by the Foreign Office, but she had spoken to him Wednesday after being contacted by journalists. "He was very shocked," she said. "It's a bit worrying".