RAF jets escorted a Kenya Airways plane into Stansted Airport where police surrounded and searched the Boeing aircraft.
Armed officers boarded the plane, according to witnesses.
It is understood the Typhoon jets took over the interception from French jets as a ‘security precaution’.
One woman said: “On flight this morning from Nairobi to London Heathrow.
“Forty five minutes before we were due to land, we were told that we’d been diverted to Stansted.
“We’ve been surrounded by all the police. They’ve all got guns all dressed in black and are ID-ing us. Captain hasn’t even said anything.”
Essex Police were called to the runway where they helped bring the flight to a remote stand.
The force said: “We are currently attending an incident at Stansted Airport.
A London Stansted spokeswoman said the Boeing 787 “landed safely with Essex Police in attendance”.
The Ministry of Defence said the jets were launched “as a precaution this afternoon to investigate a civilian aircraft which was approaching the UK”.
It said the plane “remained in contact with air traffic controllers throughout, and was escorted to Stansted Airport where it landed safely.”
The plane was diverted to Stansted just before 3.45pm.
Kenya Airways said its headquarters had “received an alert of a potential security threat on board KQ100 operating from Nairobi to London Heathrow”.
“KQ management in conjunction with the security authorities of the government of Kenya and the United Kingdom carried out a thorough risk assessment of the threat,” it said in a statement.
“The crew onboard were briefed, and all safety and security precautions were taken to ensure the safety and security of our crew and passengers on board.
“The aircraft landed safely at Stansted Airport, London, for security clearance by UK government security personnel.”
An Essex County Fire and Rescue spokesman said: “Eight crews are in attendance at Stansted Airport.
“We are working with Essex Police and the airport to bring the incident to a successful conclusion.”
Stansted is the designated airport for dealing with security issues in the UK.
