The father of senior Hamas military commander Mahmoud al-Mabhouh with a photo of his son Photo: REUTERS

The identities of six Britons living in Israel were stolen by members of an alleged hit squad which killed Mahmoud al-Mabhouh in Dubai in January. The Israeli intelligence service Mossad is widely believed to have organised the murder.

Mr Miliband spoke out after the Israeli ambassador to London, Ron Prosor, was called to the Foreign Office to discuss the affair, which is rapidly escalating into a major diplomatic crisis.

“We wanted to give Israel every opportunity to share with us what it knows about this incident,” Mr Miliband said.

“We hope and expect that they will co-operate fully with the investigation that has been launched by the Prime Minister and will be undertaken by the Serious Organised Crime Agency.”

Mr Miliband denied that the UK Government was merely “going through the motions” of asking questions about the incident.

“There’s obviously been a very serious incident involving British passports… we think it is right to have the investigation the Prime Minister has launched,” he said.

“That is not going through the motions, that is the rightful business of government.”

He added: “We want to get to the bottom of the issues of the fraudulent use passports and their potential use. That is the most important thing to do.”

Mr Prosor, who spent less than an hour discussing the matter with Sir Peter Ricketts, the head of the diplomatic service, said: “I was unable to add additional information to Sir Peter Ricketts’s request.”

Meanwhile the Israeli ambassador to Ireland insisted he knew nothing about how three faked Irish passports also came to be used by the alleged killers.

After an hour-long meeting with Irish diplomats in Dublin, Dr Zion Evrony said he was under no obligation to address the international incident in public.

He said: “I was invited to a meeting with the Secretary General (David) Cooney. I told him I don’t know anything about the event – beyond that it is not customary to share the content of diplomatic meetings.”

Dr Evrony had been summoned to the Irish Department of Foreign Affairs to explain why three genuine Irish passport numbers were on forged papers used by the 18-strong alleged hit squad.

Dubai’s chief of police has said he is now 99 per cent certain of Israel’s involvment in the killing.

Lt Gen Dahi Khalfan said the finger of blame for the assassination in Dubai last month was now almost conclusively pointing at Israeli secret service agents.

He said: “Our investigations reveal that Mossad is involved in the murder of (Mahmoud) al-Mabhouh. It is 99 percent, if not 100 percent, that Mossad is standing behind the murder.”

Conservative leader David Cameron said Tel Aviv must provide assurances that it would never sanction the use of UK papers in operations by its secret service.

Mr Cameron also called for answers from the Government about when it knew that falsified documents in the names of British citizens were used in the murder of Mahmoud al-Mabhouh in his Dubai hotel room on 20 January.

The Dubai authorities have said they contacted the British Government at the end of January to ask for assistance with the case.

“At the very least, we need some assurances about the future to make sure whatever has happened in the past can’t happen again, and I would expect the Government to ask some pretty tough questions,” Mr Cameron said.

A senior Foreign Office source told The Daily Telegraph: “If the Israelis were responsible for the assassination in Dubai, they are seriously jeopardising the important intelligence-sharing arrangement that currently exists between Britain and Israel.

“Britain has cut ties with Mossad in the past, and will do so again if the Israelis are found to be acting against British interests.”

But Israeli Foreign Minister Avigdor Lieberman has said there is no reason to believe that Mossad was involved and shrugged off suggestions that ties between Israel and Britain could be strained over the affair.

“There is no reason to think that it was the Israeli Mossad and not some other intelligence service or country up to some mischief,” he said.

“I think Britain recognises that Israel is a responsible country and that our security activity is conducted according to very clear, cautious and responsible rules of the game. Therefore we have no cause for concern.”

Dubai has now increased its list of suspects to at least 18, including the 11 people identified earlier this week, two Palestinians in custody and five others.

The official, who spoke on condition of anonymity, said that two women – one of whom travelled on an Irish passport in the name of Gail Folliard – are among the suspects.

Six British passport holders, three Irish, a German and a man with a French passport made up the alleged hit team.

The UK has said the passports they used were fake documents using the identities of British nationals all living in Israel, while Ireland said that it had never issued passports in the names of those implicated in the assassination.

But Dubai police insist the European passports were not fakes, according to a report in the local Al-Bayan newspaper.

“Dubai police has more evidence, apart from the tapes and photos that were revealed earlier,” police chief Dahi Khalfan was quoted as saying. “The coming days will carry more surprises which will leave no room for doubt.”

He said that Dubai immigration officers were “trained” by European security experts to spot such fake passports.

“This training qualifies immigration officers to spot fake passports. They applied these procedures at Dubai airport when the alleged (killers) entered the country,” he said. “No forgery was found in those passports.”

The Serious and Organised Crime Agency, which has a unit based at the British Embassy in Dubai, has begun its own investigation into the identity thefts.

Gordon Brown, the Prime Minister, has stressed the importance of protecting the status of the British passport.

“We have got to carry out a full investigation into this,” said Mr Brown. “The British passport is an important document that has got to be held with care. A British passport is an important part of being British.

“The evidence has got to be assembled about what has actually happened and how it happened and why it happened and it is necessary for us to accumulate that evidence before we can make statements.”