London ? Britain took the extraordinary step Tuesday of expelling an Israeli diplomat for the first time in more than 20 years, after concluding there was compelling evidence that Israel was responsible for the use of forged British passports in the plot to slay a senior Hamas operative in Dubai.

British Foreign Secretary David Miliband said trust between the two countries had been badly dented, demanded formal assurances it never happen again and — in an unusual step — issued travel advice to U.K. citizens warning their identity details may be at risk if they visit Israel.

Miliband told the House of Commons that the expelled diplomat, who has not been named, was removed following an investigation into the use of 12 fake U.K. passports in the Jan 20. slaying in Dubai.

“We have concluded that there are compelling reasons to believe that Israel was responsible for the misuse of the British passports,” Miliband said.

Britain’s Serious and Organized Crime Agency found the forged British passports were copies of authentic documents handed to Israeli officials for inspection either in Israel or other countries, Miliband said. He said the fakes were high-quality and almost certainly “made by a state intelligence service.”

“The actions in this case are completely unacceptable and they must stop,” Miliband said.

However, Miliband insisted Britain has drawn no conclusions over who is responsible for the killing of Hamas official Mahmoud al-Mabhouh, saying investigation by Dubai authorities was continuing.

Dubai authorities accuse Israel’s Mossad of carrying out al-Mabhouh’s killing in a luxury hotel room, and have identified at least 26 suspects in an alleged hit squad — members of which used forged European and Australian passports.

Interpol has a wanted list of 27 people in connection with the slaying. Israel has neither confirmed nor denied any involvement in al-Mabhouh’s death.

Israeli Foreign Minister Avigdor Lieberman said Israel had never been supplied with “any proof that Israel was involved in this affair” and that he regretted Britain’s decision.

Israel’s ambassador to London said he was “disappointed by the decision of the British government” but pledged that the two countries would retain close ties. “The relationship between Israel and the United Kingdom is of mutual importance,” Ron Prosor said.

France and Ireland are also carrying out inquiries into the use of four forged French and six Irish passports. Ireland’s foreign ministry said it would consider further action once an investigation with Irish police is completed.

Dubai police believe three Australian passports and a German one were also used in the killing.

At least 15 of the names used by the suspected killers match those of Israeli citizens who are dual nationals of Western countries. All have denied involvement.

Miliband said in the cases of the 12 British citizens, there was “no evidence to suggest that those 12 were anything other than wholly innocent victims of identity theft.”