Early indications suggest that a plane diverted from Manchester to Stansted Airport was not the subject of a terror attack, a British security source has said.
The Pakistan International Airlines plane, carrying 297 passengers, was escorted to Stansted by a fighter jet.
Flight PK709 from Lahore had been due to land at Manchester Airport at 1.30pm.
Police have arrested two men on suspicion of endangerment of an aircraft.
A spokesman for Stansted said the plane was being held in an isolated area and that the rest of the airport was operating as normal.
Britain's Ministry of Defence said an RAF Typhoon jet was launched to investigate an incident involving a civilian aircraft in UK airspace.
Essex Police said an incident had occurred on a flight and they were investigating.