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".

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.