Thomson and First Choice clients are being evacuated on charter flights from Kenya’s coast after the Foreign & Commonwealth Office warned them to leave because of terror threats.

Thomson said on its website that the decision to repatriate all customers currently on holiday in Kenya was a “precautionary measure”.

Both Tui Travel-owned companies said they were cancelling flights to Mombasa until at least October.

Half of the tourists were due to leave yesterday from the international airport at Mombasa, Kenya’s main coastal city. The rest were booked on a second chartered aircraft due to fly home today. The company was understood to have about 500 clients in the country.

Other British tourists booked by other companies were not being evacuated, a holidaymaker staying a hotel on Diani beach south of Mombasa and outside of the FCO’s new alert zone, told The Telegraph.

The FCO warned on Wednesday that tourists should not travel to Mombasa city or to popular beaches to its north because of the threat of terrorism, and those already there should leave immediately.

A Tui Travel spokesman confirmed that it had evacuated all its customers from Kenya “as a precaution”, including those whose accommodation was outside the FCO’s alert zone.

“The Foreign and Commonwealth Office is now advising against all but essential travel to Mombasa island, Kenya,” the company said.

“Thomson and First Choice have been continuously monitoring the situation as it developed and have been working very closely with the FCO and follow its advice at all times.

“As a result of the change in FCO advice, the decision has been taken to cancel all our outbound flights to Mombasa, Kenya up to and including 31 October.

“As a precautionary measure, we have also taken the decision to repatriate all customers currently on holiday in Kenya back to the UK.

“Our experienced overseas resort team are updating all our customers currently on holiday in Mombasa of the change in FCO advice.”

The company added that customers due to fly to Mombasa before November should contact its call centre or their travel agent.

“We understand that many customers will be very disappointed about the cancellation of their holiday to Kenya,” it said.

“However, in these types of situations we have to follow the FCO advice.”

Muriithi Ndegwa, managing director of the Kenya Tourism Board, said: “We are indeed disappointed by the FCO’s decision to enforce this advice against non-essential travel to some areas of Mombasa.

“We will work tirelessly with the British Government to demonstrate the enhanced security in place to ensure the safety of British visitors.”