Unmanned drones, similar to those used in Afghanistan, could be used by police to free up officers for other duties, it was reported.

The airborne cameras, known as unmanned aerial vehicles (UAVs) may be used over cities or big events like Glastonbury, according to a National Police Air Service director.

Superintendent Richard Watson suggested they could have been deployed during the Olympic Games but have not yet proved to be cost-effective for widespread use.

Some forces have tried the remote-controlled system, which has been dubbed "spy in the sky". A £13,000 drone was launched successfully but was later lost in the River Mersey.

In a presentation to the defence industry, reported by the Times, Supt Watson said: "I think we missed an opportunity with the Olympics. But there is an opportunity to do things differently. Until we start to ask the questions, we will always think the same way.

“I see unmanned systems as part of the future. There is an aircraft over London all the time — every day, giving images back. Why does it need to be a very expensive helicopter..?