Police in London are questioning a Venezuelan national after what appeared to be a live grenade was detected in his baggage on his arrival to Gatwick airport on a flight from Colombia.
The security alert, which began at 2.30pm, closed down the airport's north terminal.
Incoming flights have been diverted to the south terminal and a number of short haul flights have been cancelled.
Earlier, police arrested two men under Britain's terrorism act near London's Heathrow Airport.
The men were detained in the Hounslow area of west London, but it is thought their arrest was not connected to the high security alert in recent days around the airport.
