Royal wedding 2018: Aer Lingus jet 'photobombs' police helicopter monitoring crowds

Police on board a helicopter monitoring the royal wedding between Prince Harry and Meghan Markle got a shock when a commercial airliner flew beneath them.

In a tweet that quickly went viral, the National Police Air Service's Benson base posted an image of an Aer Lingus passenger jet "photobombing" their camera as they monitored the crowds in Windsor for the Royal Wedding.

"That awkward moment where you're innocently scanning crowd numbers around the Royal wedding and a plane several thousand feet BELOW us scares me for a split second!" the tweet read.

The Irish airline's plane was on final approach to Heathrow Airport when it passed over Windsor. According to the NPAS, the jet was flying at between 1000 and 3000 feet (300 and 900 metres) while the police helicopter was at 8000 feet (2400 metres).

Although there was a no-fly zone in force over Windsor during the wedding, NPAS said that police and air ambulance aircraft were excluded, along with aircraft under the control of NATS, the air traffic control service that runs operations for Heathrow airport.

The footage came from a helicopter, not a drone, as the latter aircraft are banned from flying near the airport.

"Aircraft have traffic alerting and avoidance systems, transponders, radios and an air traffic service unit orchestrating it all. A drone operator has... none of the above! It's safety, pure and simple!" the NPAS tweeted.