Flights to Heathrow were diverted or delayed this morning after the airport closed its airspace following an RAF request.
A spokesperson for the airport said the RAF use of the airspace was ‘unplanned’.
At least five British Airways flights and one Virgin Atlantic flight were diverted to other airports, while other aircraft were stacked in the sky waiting for clearance to land, according to reports.
Airspace was closed around 9am for approximately 20 minutes, although delays continued for about an hour.
Passengers onboard affected flights reported pilots said the situation was caused by a ‘security incident’, although the airport has denied this.
Passengers and Londoners tweeted about the incident, with one saying: "@HeathrowAirport Stacking all over London this morning, something happened?"
Another tweeted: "Got diverted with British Airways BA771 from Stockholm to Stansted. Still on the ground and waiting for info."
Airbus pilot Geri Moore tweeted: "Nothing like counting how much fuel you have left to the minute… but made it back to Heathrow, phew! What’s going on @HeathrowAirport!?"
Heathrow airport said: "Arrivals were paused briefly this morning due to an RAF request for an operational flight within part of Heathrow’s airspace.
"Arrivals are now operating as normal."
An RAF spokesman said: "The RAF can confirm that a flight was completed this morning by one of our assets from RAF Northolt.
"This flight was coordinated with Heathrow ATC but had to extend by a few minutes to complete its sortie. The minor delays caused to civilian air traffic are regretted."
