Britain has declared its ''outrage'' at the use of forged British passports by a hit squad that killed a Hamas official in Dubai, and sent police investigators to the Gulf emirate to collect evidence.

The officers from Britain's Serious Organised Crime Agency (SOCA) arrived in the United Arab Emirates as the investigation focused increasingly on Israel.

However, Britain's ministers are under pressure to explain whether they knew two weeks ago that a hit squad that killed Hamas leader Mahmoud al-Mabhouh had used British passports.

Speculation was mounting that the British government was aware on January 30 - 10 days after Mahmoud al-Mabhouh's murder - of a possible British link to the suspects.

Shadow foreign secretary William Hague called on the government to make a statement in Parliament about when the Prime Minister and the Foreign Secretary were told of a possible British link. Mr Hague suggested it was an ''entirely possible scenario'' that ministers knew of a British connection at the end of January.

His comments came as sources in Israel told The Daily Telegraph that Britain was ''feigning'' outrage over the abuse of passports by the hit squad, widely thought to have been from the Israeli intelligence service Mossad.

The Dubai police chief Dahi Khalfan Tamim has said he was ''99 per cent, if not 100 per cent certain'' of Mossad's involvement, and called on Interpol to issue an arrest warrant for Israeli spy chief Meir Dagan.

He said seven suspects in the killing were now in Israel.

While SOCA is concentrating specifically on the misuse of British passports, MI6 [British Secret Service] is believed to be conducting a broader, parallel probe into Israeli involvement.

Britain, Ireland and France stepped up diplomatic pressure on Israel, demanding explanations on the use of forged European passports by the assassins.

But Israeli envoys in London and Dublin said they had nothing to say about the affair, bringing closer the prospect of a high-level diplomatic row.

The Israeli embassy made no comment on its meeting at the French Foreign Ministry, which ''expressed its deep concern about the malicious and fraudulent use of these French administrative documents''.

The US also appeared likely to be drawn into the affair for the first time, after The Wall Street Journal reported that Mabhouh's assassins had used US-registered credit cards to buy airline tickets.

British Foreign Secretary David Miliband said the Israeli ambassador to London, Ron Prosor, had been asked to shed light on how the identities of six British citizens living in Israel had been stolen and used by the assassins. He said any tampering with British passports was ''an outrage''.

''We wanted to give Israel every opportunity to share what it knows about this incident and we hope and expect that they will co-operate fully with the investigation,'' he said.

Irish Foreign Minister Michael Martin revealed that a further two Irish passports were used in the assassination, bringing the number of Irish travel documents involved to five as speculation grew that the size of the hit squad was bigger than the 11 originally reported.

Mr Miliband is to meet his Israeli counterpart, Davigdor Lieberman, in Brussels on Monday.

Mr Lieberman has insisted there is no proof of Israeli involvement, and stressed that his government employed a ''policy of ambiguity'' on intelligence matters.

GUARDIAN, TELEGRAPH, BLOOMBERG