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Police chiefs are investigating counter measures amid the “threat posed by drones” straying ito restricted London air space.

It comes as Met officers probe what was believed to be Britain’s first unmanned aerial vehicle strike against a plane, which was on a landing approach to Heathrow airport.

Scotland Yard said “an object believed to be a drone” hit the front of a British Airways Airbus A320 last Sunday lunchtime above Richmond Park.

There were 132 passengers and five crew on board the flight approaching from Geneva, which was at 1,700ft - the legal maximum height for UK drones is 400ft.

BA said the plane landed safely and was cleared by engineers for its next flight.

Transport minister Robert Goodwill played down the incident, telling Parliament on Thursday it could have been a “plastic bag”, but Scotland Yard told the Standard on Friday that officers still believed the object was a drone.

Last year, remote controlled drones had near misses at Heathrow, City, Gatwick and Stansted.

Heathrow refused requests for an interview on its anti-drone measures, referring enquiries to the police.

Asked about how it was securing London’s skies, the National Police Chiefs’ Council would not reveal specific details about counter measures being tested, only they were “working with partners to better understand the threat posed by drones and to develop an appropriate technical response”.

"Trying to work out what a standard test for a drone strike is going to be more challenging" Drone expert Lambert Dopping-Hepenstal

The Government has already undertaken trials of counter-UAV systems, including one using military-grade technology deployed in Afghanistan that downs unmanned aerial vehicles with a “death ray” jamming its radio signals.

The Anti-UAV Defence System is collaboration between three British companies, costs “under a million pounds” and participated in government counter-drone tech trials last summer.

It tracks heat from a drone’s battery pack, zooms in using a powerful camera and can down it by blocking the signal from up to six miles away, before tracing the owner.

Mark Radford, chief executive of one of the trio of firms, Blighter Surveillance Systems, said: “It allows us effectively to take control of that drone to control whether we force a crash landing or return it home to the take off site so the police or security forces can intercept the operator.

“One of the scenarios is use at airports and in urban areas.”

Hunting eagles and net-firing bazookas have even been mooted as possible solutions for knocking out rogue UAVs.

Drone manufacturer DJI has developed geo-fencing software that blocks its UAVs from buzzing into sensitive airspace, such as airports and prisons.

Sussex Police, which runs Gatwick airport’s security, have their own squadron of Aeryon SkyRanger quadcopters that fly up to 400ft high.

Inspector Mark Callaghan, drones spokesman for Sussex Police, said their UAVs help “support aviation security around the airport confines”, assisting patrols to secure the perimeter, but do not knock out drones straying into Gatwick’s airspace.

Plane manufacturers are also being challenged to calculate what will happen if a drone is sucked into a jet engine because of the evolving shapes and weights of UAVs, a leading aerospace engineer said.

Lambert Dopping-Hepenstal, of the Institution of Engineering and Technology, said: “Civil aircraft are tested for bird strikes, they have a requirement that when a certain sized bird, if ingested into engines or the bird hit the air frame, it’s not catastrophic.

“The problem is trying to work out what a standard test for a drone strike is going to be more challenging.”

He added: “Already some drone manufacturers instal geo-fencing, a software programme using its GPS navigation system which says basically says you can’t fly in restricted areas.

“Even if the person tried to fly there the thing wouldn’t take off or would bounce back off the imaginary wall.”