British police arrested two men on a Pakistan International Airlines flight on Friday on suspicion of "endangerment of an aircraft", after it was escorted to a different airport by fighter jets.
The plane had been flying from Lahore in Pakistan to Manchester, before it was diverted to Stansted, in Essex, southern England.
Flight PK709 from Lahore in Pakistan had been due to land at Manchester in northern England with 297 passengers on board, but was diverted shortly before arrival. A security source said early indications were that the plane was not the target of a terrorist attack.
Britain is on high alert after a soldier was hacked to death on a London street on Wednesday in what the government are treating as a terrorist incident.
"Essex Police have boarded a passenger plane diverted to Stansted Airport and two men have been arrested on suspicion of endangerment of an aircraft. They have been removed from the plane," the police said in a statement. The force is responsible for the area where Stansted is located.
Stansted is one of London's less busy airports, preferred as a location for handling airplane security incidents. A spokesman for the airport said the plane was being held in an isolated area and no one had been hurt, and that the rest of the airport was operating as normal.
Essex County Fire and Rescue Service said 10 fire engines had been sent to the airport.
The Pakistani plane was a Boeing 777, according to the flight tracking website www.flightradar.com.
Britain launches military planes to intercept unidentified aircraft when they cannot be identified by other means, for example, when the aircraft is not talking to air traffic controllers.
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A passenger aboard the plane said someone had made threats against its crew.
"We landed safely and then he [the pilot] announced that they had had some kind of threat from someone and that's why he landed the plane," the passenger, identified only as Munsif, told BBC television.
Munsif said he was sitting at the front of the plane, but that the incident had happened at the back.