Image caption The drones being considered are small enough to fit into a rucksack

Police aerial surveillance in Northern Ireland may be about to take on a whole new form - one that belongs more to the world of sci-fi and the future.

The PSNI is considering the use of mini drones to combat crime and the dissident republican threat.

They are not the large missile carrying drones used by the US military.

It is understood the models being considered are small enough to fit into a rucksack and can be assembled and deployed within minutes.

The manufacturers of one of these unmanned aerial vehicles, known by the military as UAVs, say it snaps together as easily as children's building blocks.

It might look like a toy - but it's anything but.

'Game-changing'

It is fitted with a camera that automatically tracks a subject, can relay live pictures back to the operator, has a three kilometre range and flies at ground speeds of 50 kilometres an hour.

The UAVs are described as game changing technology - policing from the sky. Indeed, one source told me they could act as modern day watch towers.

Security sources say border areas like south Armagh are where the use of the technology would be most valuable because they can cover large areas at a fraction of the cost of a helicopter.

They are not so easy to use in built-up urban areas, where they're also governed by tighter regulations.

Because of potential risks to other aircraft and people on the ground, the Civil Aviation Authority must grant permission for UAVs to take to the skies.

The CAA has confirmed to the BBC that it has already had discussions with the PSNI about possible drone deployment.

The drones, or UAVs, used by law enforcement agencies around the world, have already been deployed by some UK police forces.

River crash

But there have been problems. A drone used by police in Liverpool crashed into the river Mersey. In addition there were red faces when police discovered they hadn't obtained the necessary CAA permission.

At a time when policing budgets are under pressure, there is a strong economic argument for their deployment.

The latest police helicopter cost £7m when it was bought last year.

Adding up the figures, maintenance, fuel and pilot salaries, running the police's fleet of three helicopter costs over £1.5m every year.

A police drone could cost at most £150,000 and, powered by batteries and able to remain airborne for up to seven hours, the running costs are substantially lower.

In a statement to the BBC, the PSNI said it constantly reviews the availability of new equipment and technology but at this stage has no immediate plans to buy any UAVs.

Earlier this year, the police were given a quarter of a billion pounds of additional funding to combat the threat from dissident republicans.

If the police decide to deploy UAVs, they have the option of using some of this special security fund, or finance the purchase from the normal policing budget.