Six more British passports were used in the assassination of a Hamas leader in Dubai, it was revealed today.
That brings the total used in the hit on Mahmoud al-Mabhouh in the Gulf state last month to 12.
Investigators from Britain's Serious Organised Crime Agency are probing the use of cloned British passports in the attack, which has been linked to agents of the Israeli secret service, Mossad.
A Soca spokesman said: "We have been informed by the Emirati Authorities that there are six additional UK passports that are subject of their enquiries.
"The genuine passport holders have not been confirmed as being directly linked to the murder.
"Soca are currently working to identify the location of these individuals and are pursuing lines of enquiry in regard to this new information but it would not be appropriate to comment as this is an ongoing investigation."
The six new British passports are among those used by a group of 15 new suspects travelling on British, French, Irish and Australian passports, Dubai police said.
The innocent passport owners were named in reports as Daniel Marc Schnur, Gabriella Barney, Roy Cannon, Stephen Drake, Mark Sklur and Philip Carr.
The new revelations increase the total number of suspects to at least 26.
Al-Mabhouh, who founded Hamas's military wing, was killed in his hotel room on January 19.
It is thought he was trailed to his room by members of the hit squad who wore fake beards, wigs and other disguises.
Dubai officials have said they are "99% certain" that Mossad was behind the murder, although Tel Aviv has refused to confirm or deny the link.
In the House of Commons today Gordon Brown said questions had to be answered about the misuse of British passports, but refused to draw "immediate conclusions" about what happened without seeing the evidence.
SDLP MP Mark Durkan accused the Israeli authorities of treating the Government with "disdain" over the allegation.
But Mr Brown told him: "I can assure you that where there are questions about the misuse of British passports they have to be answered.
"We have set up and there is an investigation ongoing into the very incidents you have raised.
"I would not draw immediate conclusions without seeing the evidence and I think it is important to see the evidence on this before any further conclusions are made.
"But I do agree with you we do not support state-sponsored terrorism in any country."
This week Foreign Secretary David Miliband sought answers in a 45-minute private meeting with his Israeli counterpart Avigdor Lieberman who told the Foreign Secretary he had "no information to give" at this stage.