The Boeing 777 is en route from Las Vegas.
British Airways flight BA2276 declared a general emergency on approach to London, more than nine hours after taking off from the US.
The flight was scheduled to take off at 5.40pm but started on its journey 42 minutes behind schedule.
Its pilot sounded the Squawk 7700 call – the aviation term for a general emergency – over the north of England.
The emergency call comes just moments after the UK was rocked by an RAF Typhoon sonic boom scrambling in response to a bomb threat on board another flight today.
A woman was arrested earlier this week after allegedly sparking a hijack alert while dashing for the cockpit of a Jet2 plane – forcing the RAF to scramble two Typhoon fighter jets to escort it – has been released on bail.
Jet2 said there had been an “extremely disruptive passenger” on board its flight from Stansted to Dalaman in Turkey on Saturday, forcing the aircraft to return to the Essex airport.
The two Typhoon fighter jets caused a sonic boom as they escorted the plane back to Stansted Airport, prompting people to call 999 as they feared there had been an explosion.
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