The phone, which rang about an hour into the flight, was pounced upon by crew who feared that it was being used to try to detonate a bomb on the aircraft, bound for New York. None of the 217 passengers claimed the handset. They had been banned from carrying hand luggage, including mobile phones, as part of tighter security measures.

The captain returned the Boeing 777 to Heathrow where further security checks were carried out on the aircraft and its passengers. Ted and Veronica Carlisle, who were among those on board, said that when cabin crew heard the ringing they scrambled to “cover it with blankets and pillows and whatever else they could grab”. Mrs Carlisle, from Oklahoma, added: “It was nerve-racking, but people supported the decision to turn back to London.”

Although the captain, who contacted BA’s security team at Heathrow, was given the all clear to continue, he decided to dump fuel and return to London.

It was believed that the phone was left by a passenger who had flown into Britain, and so had not been subject to the extra security measures.

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