The engine burst into flames soon after take-off from Los Angeles but BA advised the pilot by radio to continue for 5,000 miles to Heathrow on the Boeing 747’s remaining three engines.

As the aircraft approached Britain, the pilot was forced to divert to Manchester because he feared that he would run out of fuel. A few minutes before touchdown, he declared an emergency and was met on the runway by four fire engines and thirty firefighters.

The aircraft, carrying 351 passengers, had been unable to climb to its cruising altitude of 36,000ft and had to cross the Atlantic at 29,000ft, where the engines perform less efficiently and the tailwinds are less favourable. The unbalanced thrust also meant that the pilot had to apply more rudder, causing extra drag.

The Federal Aviation Administration criticised BA strongly for allowing the flight, in February last year, to continue. It said that the aircraft should have returned to Los Angeles and is proposing to impose its maximum fine of $25,000 (£13,000) on BA for flying an aircraft in an “unairworthy condition”.

The Air Accidents Investigation Branch report on the incident, published today, identifies a conflict between US and British safety rules, and orders the Civil Aviation Authority to work with the administration to produce “clear guidance” for airlines.

BA’s existing policy, approved by the authority, states that a 747 with a failed engine should continue to its destination if the captain believes the aircraft to be safe.

The administration only allows the pilot to proceed “if he decides that this is as safe as landing at the nearest suitable airport”.

The administration said that it would have been safer to land back at Los Angeles than continue flying for 11 hours with a failed engine. “When you lose an engine you have lost your back-up. We would expect the pilot to land at the nearest suitable airport,” an official said.

The authority said that it would hold talks with the administration with a view to producing a common policy. “We are going to accept the recommendation. We will be talking to the FAA and other interested parties to try to move it forward so there is a more common policy,” an official said. BA said: “We are pushing the CAA and FAA to agree a policy which everyone can sign up to.”

The report says that BA allowed flights by 747s to continue after an engine failure on 15 occasions since April 2001. Each time, BA saved up to £100,000 that it would otherwise have spent in compensating passengers and providing a replacement aircraft.

The report also says that BA failed to give its pilots adequate training in handling fuel shortages after engine failures. The report added that BA had accepted the criticism and had improved its training programme.

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