The world's most wanted terrorist, Osama Bin Laden, has been tracked down and the SAS, Britain's elite soldiers, are poised to seize him in his secret mountain lair in Pakistan, a leading London tabloid claimed on Sunday.

Working closely with US forces, the SAS have hemmed Laden into a remote mountain area measuring just 16 km wide in Pakistan bordering Afghanistan, Sunday Express claimed.

The man believed to be responsible for the September 11 terror attacks is reportedly being guarded by 50 of his most loyal supporters who have pledged to lay down their lives for him.

The report quoted a US intelligence source saying last night: "He is boxed in."

According to the report, SAS and US special forces are awaiting orders to swoop on the world's most wanted man in the desolate Toba Kakar mountains in Pakistan's northwest frontier.

American military chiefs are confident that bin Laden -- who is believed to be holed up with Taliban leader Mullah Mohammed Omar -- cannot escape. But British planners have warned against overconfidence.

According to the report quoted to defence sources in London, the UK is reluctant to get drawn into a full-blown 'spring offensive' to wipe out the remnants of Al Qaeda, although US President George W Bush favours the move as a boost to his re-election prospects in November.

The first tip-off came from a senior Republican close to both the White House and the Pentagon, who summoned the 'Sunday Express' to a secret breakfast meeting during a flying visit to Britain last week. 

The source said: "They have found bin Laden. They now know where he is within a manageable area, which can be watched and controlled. They can see everything that goes in and out of the area. If he moves, we will know about it."

The report said bin Laden moved to the area located north of the town of Khanozai and the city of Quetta, a hotbed of bin Laden support, a month ago, from an area 240 km to the south.

The breakthrough comes at a crucial time for MI6, British intelligence agency and the CIA, both under pressure over the failure to find Saddam Hussein's weapons of mass destruction.