The cell is led by Fazul Abdullah Mohammed, a terrorist responsible for the deaths of nearly 300 people in three attacks in Kenya in the past five years. His face was on the front of all the English-language newspapers that the tourists were reading on their sunchairs yesterday.

What they did not know was that Mohammed had brought with him six other highly trained al-Qaeda operatives. They include Sheikh Ahmed Salim Swedan and Fahid Mohammed Ali Msalam, who helped him to bomb the US embassies in Kenya and Tanzania in 1998.

Details of Mohammed’s latest plot have been gleaned from the interrogation of Suleiman Abdalla Salim Hemed, a senior al-Qaeda leader snatched in a CIA operation from his hospital bed in Mogadishu, in neighbouring Somalia, in March.

He has been taken to America and is believed to have told his captors that this time Osama bin Laden’s organisation was targeting Britons. Bin Laden said in his latest recorded messages that Britons would be among al-Qaeda’s targets. That threat has intensified after Britain’s prominent role in the conflict in Iraq and Tony Blair’s close links with President Bush in the war on terrorism.

More information was obtained from Mohammed’s father-in-law, an Islamic cleric seized earlier this week from his home near Mombasa.

The cleric claims not to have known that Mohammed had returned to the resort city. The terrorist was seen prowling around the perimeter of Mombasa international airport on Wednesday afternoon.

Mohammed and his accomplices attempted to shoot down an Israeli charter flight with a shoulder-held SA70 missile last November as it took off for Tel Aviv. The Kenyan authorities have since done nothing to improve security around the airport.

The next British charter flight due to land there would have been a Monarch airline Airbus carrying more than 250 holidaymakers next Monday lunchtime. As with the Israeli charter, this flight arrives and leaves at exactly the same times every week, making it an easy target.

Jake Grieves-Cook, chairman of the Kenya Tourism Association, said his Government urgently needed to step up security at its airports to reassure travellers. Down the coast yesterday, in the hotels along the beaches of the Indian Ocean, British tourists who could have been blown up on their homeward journey simply carried on enjoying themselves.

“I am quite happy to stay here and be a pool attendant,” said John Heathcote, a retiree from Chesterfield, as he gestured at the large pool of the Turtle Bay beach resort. “Terrorists are not going to rule my life. This sort of thing is not going to stop me going on holiday. Travel companies have said they don’t know how to get us all home. Well, that’s fine by me for a little while.”

Ben Cook, 27, from Norwich, said: “"We have had a brilliant time and this can’t spoil it. All the booze and food here is unlimited, so we are just going to get stuck in.”

British tour operators were meanwhile trying to contact other British holidaymakers in Kenya, including those on safari, to warn them of the terrorism alert and flight ban.

The tourists have been told that seats on flights run by non-British airlines will be arranged as close to their planned departure date as possible. The operators have agreed to pay the extra costs incurred for holidaymakers forced to stay on in Kenya for a few additional days while enough seats on aircraft are found.

Tourists have also been told that if they are unhappy about flying from Mombasa, or either of the other two Kenyan international airports, flights from neighbouring countries will be booked for them. Security at the British High Commission, the British Airways office in Nairobi and other obvious targets was conspicuous. About 100,000 Britons visit Kenya each year — more than any other foreign nationality — and there are well over 25,000 British passport-holders in the country.

Many of those were hunkering down this weekend. “I am staying at home and keeping a low profile,” said Aidan Hartley, a long-term Kenya resident. “No one could persuade me to even get on an internal flight at the moment.”

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