A Sri Lankan Airlines plane from Colombo to Heathrow Airport was forced to make an emergency landing on Friday evening after two male passengers were suspected of "endangering" the aircraft.
The flight was diverted to Stansted and the men were arrested, police said.
According to the BBC, the A330 Airbus was carrying 267 passengers and crew. The remaining passengers were taken to a reception centre and later transferred to Heathrow.
The Independent reports that police said on Saturday that it was a criminal matter and not suspected terrorism.
They gave no details as to what the suspects were doing on the flight.
According to Sky News, the men are British nationals, aged 49 and 57.
The 49-year-old was taken to hospital and treated for a medical condition.
An Essex Police spokesman told the BBC: "Officers boarded the aircraft and arrested two men on suspicion of endangering an aircraft.
"The 49-year-old is currently receiving medical treatment in hospital and the other is in custody at Harlow police station.
"They will be interviewed by detectives. The incident is being treated as a criminal investigation.
A Stansted Airport spokesman said: "A Sri Lankan Airlines Airbus A330 diverted into Stansted at approximately 19.30 this evening [Friday].
"The aircraft, which was flying from Colombo to Heathrow, landed safely with Essex Police in attendance."
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