Intelligence chiefs believe that the plane, which crashed last weekend killing 224 people, was brought down by a bomb planted by an offshoot of ISIS in the Sinai peninsula.

The group's frontman, Abu Osama al-Masri, an Egyptian cleric, brokered a pact with ISIS last year in Syria.

Whitehall officials confirmed this weekend that Masri is a “person of interest" and that Britain would help Egypt or Russia in a “kill or capture" mission. Such a move could involve the deployment of the SAS to Egypt.

Intelligence officials believe that Masri's group, Sinai Province, used an airport insider to smuggle a bomb into the luggage hold of the Metrojet aircraft last Saturday. It is feared the mole is still at large, the report said.

Last night officials were investigating if any Britons allied to ISIS were involved after claims that the security services had intercepted “chatter" between extremists with London and Birmingham accents in the aftermath of the explosion, it said.

Yesterday, Egyptian crash investigators admitted that an unexplained “noise" was heard on the cockpit voice recorder in the final second before the Metrojet airliner came down.

They said “all possible scenarios" — including mechanical failure — were still being considered as the reason for the crash.

French media, however, reported that the noise heard on the recorder was consistent with a bomb.

Masri, 42, is a former scholar of the al-Azhar University in Cairo, a 1,000-year-old Sunni Muslim institution.

In November 2014 his Sinai-based organization pledged allegiance to Abu Bakr al-Baghdadi, the self-proclaimed ISIS caliph, in return for weapons, finance and potential bomb-making know-how.

Sinai Province has repeatedly claimed responsibility for last weekend's plane crash .A Twitter account used by the group hinted last Saturday that a bomb rather than a missile was involved.