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Some of the sightings of drones at Gatwick Airport before Christmas were in, or close to, takeoff and landing zones, the Â鶹ԼÅÄ understands.

Their appearance in critical areas underlines the threat to aircraft.

The incident caused severe disruption for two days, leaving tens of thousands of passengers stranded.

Although no shots were fired at drones during the incident, Whitehall sources say armed police were ready to attempt to shoot the drone, or drones down.

On Tuesday departures at Heathrow were temporarily stopped after a drone was reported to have been sighted.

Even before the incident at Gatwick, Heathrow Airport was trialling anti-drone systems, used to both detect drones and potentially take them down mid-flight.

The suspension of departures on Tuesday evening highlights how a determined criminal can still breach an airport's perimeter with a drone, even if there is advanced technology in place.

The Government is now considering implementing military-grade anti-drone equipment at all major UK airports, as well as other critical infrastructure such as power stations and prisons.

Some drones can travel at speeds in excess of 100 miles per hour, so hitting them mid-flight is hard and potentially risky in a built-up area like an airport.

On Thursday, the Aviation Minister, Baroness Sugg met UK airport bosses to discuss the technology already in use and how airports can beef up their defences.

Extra equipment has been installed at Heathrow since Tuesday's sightings.

Earlier, the Transport Secretary Chris Grayling told MPs that foreign airports had contacted his department to learn lessons in the wake of the chaos caused at Gatwick.

The Â鶹ԼÅÄ understands that discussions have been held with major American airports, such as New York's JFK and Dulles in Washington, as well as other major European airports.

No credible arrests have been made in relation to the drone sightings at either London airport.

The police are understood to have photos of the drone or drones used at Gatwick.