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Unmanned drones are "undoubtedly" being used to harass people, police say.

A House of Lords committee was told the devices were also being flown in protected airspace and that officers found it difficult to identify the people responsible.

The warning came from Ch Insp Nick Aldworth, of the Metropolitan Police, who is part of a nationwide group tasked with looking at the issue.

Civilian use of the aircraft, which can be legally flown, is increasing.

Drones, which are officially known as Remotely Piloted Aircraft Systems, range in size from small craft operated by enthusiasts, TV companies, police forces and surveyors and weighing a few kilograms, to larger military versions.

Smaller ones can be flown without special permission although restrictions apply if they are used in congested areas or near people's homes.

'Nefarious reasons'

The Lords Internal Market, Infrastructure and Employment Committee has been holding an inquiry into their use by civilians.

Ch Insp Aldworth said the devices, which he described as "things that fly and do not have pilots in them", could be used in a "reckless" or "malicious" way.

Baroness O'Cathain, the committee chairwoman, said a number of concerns about privacy had been raised, but Ch Insp Aldworth said this was not a police matter as there was no criminal privacy law.

However, he said other legislation could be used, for example laws banning voyeurism, in the event of drones with cameras "hovering outside people's bedrooms for whatever nefarious reasons".

Footage posted posted on the internet was the most common way of drone use coming to light, he said, and the peers were told of the difficulties of finding the people responsible.

If a drone "whizzes past your window and catches something that you would rather it didn't catch", he said, it was difficult to catch the person flying it unless the police arrived immediately.

Ch Insp Aldworth said his group's task was to find a "sensible application" of existing laws to control the use of the drones.

He said there was no doubt drones had been used in London and around the UK, pointing to footage posted of football stadiums which he said was a contravention of air navigation rules as well as being a potential safety risk if a device fell from the sky.

Criminal conduct

"We also know it has been used to embarrass people - either VIPs or members of the public," he said.

Ch Insp Aldworth said a drone had been flown as a protest in front of German Chancellor Angela Merkel, and that he expected "copycat behaviour" in the UK.

He added: "The concerns are really around the fact that we are seeing this technology being used for criminal conduct.

"We have undoubtedly seen it flown in controlled airspace, we have undoubtedly seen it used to harass people, and we have seen it flown in contravention of the air navigation orders, so I think that concern arises by the fact that there is clearly a means of offending that we do not seem to be able necessarily to address quickly."

With Christmas approaching, and prices expected to drop, use of the drones could increase, he added.

Last month, pilots' association Balpa told the committee remote aircraft the same size as small passenger planes could be operated commercially in the UK within 10 years, and called for strict controls over their use.