Foreign Secretary David Miliband has confirmed British passports used by assassins who killed a Hamas leader in Dubai were old passports which did not contain microchip technology.
Mr Miliband said they were taking allegations of misuse of British passports very seriously.
He said: “The Permanent Secretary made clear how seriously we take any suggestion of fraudulent use of British passports, he also explained the concern that we have for British passport holders in Israel whose concerns have been well expressed by them, and we’re offering them consular support.
"We wanted to give Israel every opportunity to share with us what it knows about this incident and we hope and expect that they will cooperate fully with the investigation that has been launched by the Prime Minister and is being undertaken by the Serious and Organised Crime Agency.
He said he would be discussing the matter further with Israeli Foreign Ministry officials in Brussels next week.
He added: "The integrity of the British passport is something that matters to you and me and every other British citizen.
"The passports that were used in this case did not have the new chip technology that would make it much more difficult for them to be abused, but obviously we need to make sure that the British passport remains something that everyone has confidence in and countries around the world have confidence in as well."
Israel’s ambassador Ron Prosor was tightlipped about the content of the discussions which lasted a mere 26 minutes.
A statement released by the Israeli embassy said: “Whilst of course happy to cooperate with Sir Peter’s request, I was unable to shed any further light on the events in question.
“In keeping with standard diplomatic practice, it would be improper to disclose the content of such bilateral discussions between our countries.”
Mr Prosor met Permanent Under Secretary Peter Ricketts at the Foreign Office to discuss the killing of a Hamas leader in Dubai, where the British passports of Israeli immigrants were used to conceal the identity of some of the killers.
At least seven of the members of the Dubai assassination team, who killed Mahmoud al-Mabhouh, had passports with the names of real people, six British and one German. All of the “real names” were men who had made aliyah to Israel.
Israel’s ambassador to Ireland, Zion Evrony, has also been called to a meeting at the Irish Department of Foreign Affairs in Dublin in connection with the three fake Irish passports used in the assassination.
Mr Evrony met Irish Secretary General David Cooney and the Assistant Secretary in charge of the Passport Office, Ray Bassett.
A spokesman for the Irish Department of Foreign Affairs said: "It was stressed that, regardless of who was responsible, the Government takes grave exception to the forgery and misuse of Irish passports which could devalue the standing of the passports and potentially put at risk the safety of Irish citizens travelling abroad."
The British passport holders named by Dubai police are Stephen Daniel Hodes, Melvyn Adam Mildiner, Paul John Keeley, Michael Lawrence Barney, James Leonard Clarke, and Jonathan Louis Graham.
All have expressed shock at their identities apparently having been stolen.
Mr al-Mabhouh was found suffocated in his hotel room. CCTV footage released of the assassination shows the assassins following him in the elevator and checking into a room across the hall.