Gordon Brown has called for an inquiry into how British passports were used by assassins who killed a senior Hamas leader in Dubai.

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. Most of the “real names” were men who had made aliyah to Israel.

Prime Minister Brown said: “We have to carry out a full investigation into this. The evidence has to be assembled about what actually happened, about how it happened and why.

"The British passport is an important part of being British and we have to make sure everything is being done to protect it."

Mr Brown did not say whether British intelligence believed that the passports had been used by Israeli intelligence agency Mossad.

But the former LibDem leader Sir Menzies Campbell was more forthcoming. He has demanded that the Foreign Office summons Israeli ambassador Ron Prosor for an explanation.

He said: “If the Israeli government was party to behaviour of this kind it would be a serious violation of trust between nations.”

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 of them are immigrants to Israel who have expressed shock at their identities apparently having been stolen.

The gang, wearing tennis clothes, and some in glasses, fake beards and wigs are now said to be on the run. They are believed to have arrived on separate planes and spent less than a day in the country.

Other members of the gang were using Irish, French and German passports.

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.

Four of the assassins broke into his room while he was out and pounced on his return.

Dubai has allegedly told Hamas to steer clear of the investigation, but Hamas has opened its own inquiry with the help of Syria and Iran. Hamas would not confirm that Mr al-Mabhouh had been en route to Iran.

In 1997, Mossad agents were caught using Canadian passports during a failed assassination attempt on Hamas official Khalid Mashall in Jordan.