The Foreign Office has categorically denied it was warned hours before about a high-profile assassination, and that British passports would be used by Mossad.

Although the target, Hamas military leader Mahmoud al-Mabhouh, and the location, a luxury hotel in Dubai, were not named, a Mossad source allegedly told the Daily Mail that MI6 knew the January killing was imminent.

The Foreign Office, however, insists that ministers knew nothing about the six British passports, used to cover the identities of the assassins, before the names were released by Dubai police.

A Foreign Office spokesman said: “Any suggestion that we knew anything about the murder in Dubai before it happened, including about the misuse of British passports, is completely untrue.  

“As we have said already, the Dubai authorities told us about the role of British passports on February 15, several hours before their press conference. 

“We told them the following day that the passports used were fraudulent. 

“The head of the Dubai police has also made clear that embassies were not contacted until shortly before the identity of the suspects was revealed.”

The Mossad agent reportedly said that British ministers were “going through the motions” by calling in the Israeli ambassador Ron Prosor yesterday.

Dubai police chief, Dahi Khalfan Tamim, has said he is almost “99 per cent certain” that the killing of Mr al-Mabhouh was the work of Mossad.