The first 24-hour police drone unit is to be launched, amid fears that forces may have to rely on them because of falling officer numbers.

The ‘flying squad’ will pursue suspects, find missing people and help solve murders. Assistant Chief Constable Steve Barry, national spokesman on drones, predicted forces across Britain would soon be using them as they are cheaper than helicopters and can perform some duties of bobbies on the beat.

But the move has prompted privacy concerns and warnings that the technology should ‘never be an excuse to cut officers’.

Devon and Cornwall Police has advertised for a drone manager to lead its new dedicated unit, which will be launched in the summer and shared with Dorset.

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Devon and Cornwall Police will launch a dedicated 24-hour police drone unit to save costs on helicopters. Pictured is an officer controlling a drone that recently watched over the Duchess of Cambridge during a royal visit

Sussex and Surrey are considering whether to set up full-time units. For now, officers in other roles operate drones part-time.

In total 21 forces are experimenting with the technology, known as unmanned aerial vehicles, to carry out an array of duties – from everyday search missions to watching over the Duchess of Cambridge on a royal visit and pursuing a lynx that escaped from a zoo.

But there are concerns that the relatively cheap remote-controlled devices could lead to officers being cut in future.

Mr Barry, National Police Chiefs’ Council lead on drones, admitted they may give an opportunity for chiefs to ‘rationalise’ whether it is cheaper and more efficient to send a bobby or a machine.

He said of the new unit: ‘I would not be at all surprised if other forces follow in due course – the question is not whether they will, it’s when.’

Asked whether chief constables might be tempted to cut officers if drones prove a success, he said: ‘There may be an opportunity at some point in the future to rationalise what we need our cops to do because we find drones can do it more effectively and more cost-efficiently … an example of that would be looking for missing people.

‘That opportunity has not yet manifested … There will be a point where that question gets asked.’

But he also said: ‘I think it’s a brave senior officer who will make that step that is going to cut cops because they have got drones.’

The drones are expected to be a 'significant piece of kit' and Devon and Cornwall will share the first unit with their counterparts in Dorset. Pictured is a Merseyside Police officer operating a surveillance drone in Liverpool

Mr Barry, who works for Sussex Police, added: ‘If delivering the best service within the budget means using drones for something, a cop is now free to go to that burglary. It’s about freeing resources.’

Devon and Cornwall Police covers the largest force area in England. Its drone fleet will allow it to respond to incidents more quickly as UAVs can be dispatched in a fraction of the time it would take officers to cover that ground.

Dorset police and crime commissioner Martyn Underhill has said drones ‘have the capability to revolutionise the way we police’, adding: ‘There is no reason why [they] can’t become as familiar a sight as patrol cars, a police helicopter or an officer on the beat.’

Chief Superintendent Jim Nye, strategic alliance commander for operations in Devon, Cornwall and Dorset, said drones were going to be a ‘significant piece of kit’.

He stressed that the force has no plans to cut officers, adding: ‘I see it as an opportunity to improve technology available to police to better do what we do.’

Drones will slash bills for forces. A helicopter flight costs an average of £1,266, while a drone can be bought for as little as £1,000, after which the only operating cost is recharging the battery.

They can be used to photograph and video crime scenes or monitor protests, sieges and football matches, and have been tested for use in terror attacks and to track anti-social behaviour.

The machines can also save officers from danger by peering over a cliff face to look for a fallen walker, for example.

Police have even deployed hi-tech drones to protect the Duchess of Cambridge during royal engagements.

Last month, South Wales Police used a £989 device to survey the location remotely from the air during her visit to a charity in Torfaen.

A force spokesman said: ‘Using a drone will allow officers to gain vital information.’

Drone video recordings have begun to feature in court proceedings to help jurors visualise where a crime happened.

Police are also using drone images to map road accidents, and are exploring how they could be tethered to provide permanent cover in areas where CCTV is not available.

The NPCC is preparing a report on the results of drone trials, and the National Police Air Service is due to submit a £70,000 funding application for drone ‘centres of excellence’.

Phill Matthews, of the Police Federation representing rank and file officers, said the devices will ‘free up beat bobbies’, adding: ‘It’s inevitable given the squeeze on finances that forces will seek to utilise technology as a means to meet what they have to do cheaper.’

But ex-Scotland Yard officer Rory Geoghegan of the Centre for Public Safety said it would be a ‘nightmare scenario’ if drones were sent to probe crimes such as burglary.

He added that it would be ‘foolish to think that you can do away with the fundamentals – you need bobbies on the ground. It should never be an excuse to cut officers.’

Daniel Nesbitt of campaign group Big Brother Watch said: ‘Drones can be very intrusive so the public has to be informed about how they are being used … and if they aren’t effective then the police should stop using them.’

Alex Wild of the TaxPayers Alliance said ‘a close eye’ must be kept on costs as the public sector had ‘a poor record in getting value for money’ for new technology.