91�ȱ�

Drones could be used by terrorist groups as "simple, affordable and effective airborne improvised explosive devices," says a report by London-based think tank the .

The authors suggest manufacturers should program drones with the GPS coordinates of no-fly zones.

The British government should also relax regulations on radio frequency jammers, they add.

In addition, they advise tighter UK licensing regulation.

Currently in the UK, anyone can own and operate for non-commercial purposes a drone that weighs less than 20kg (3st 2lb) - and there are hundreds on the market.

"A range of terrorist, insurgent, criminal, corporate and activist threat groups have already demonstrated the ability to use civilian drones for attacks and intelligence gathering," the report reads.

"The best defence against the hostile use of drones is to employ a hierarchy of countermeasures encompassing regulatory countermeasures, passive countermeasures and active countermeasures."

It suggests that these could include:

However, David Dunn, professor of International Politics, at Birmingham University, told the 91�ȱ� that licensing may not deter terrorists.

"Law abiding citizens are likely to register, but it would be very difficult to stop terrorists and other criminals from purchasing drones abroad and then using them here," he said.

"Up until now it was expensive and required skill to be able to fly an aircraft - which acted as a form a regulation in itself.

"Now, you can fly these things relatively easily over people's heads."

The report also lists recent examples of suspicious activity involving drones:

The authors of the report, members of a non-profit group called Open Briefing which describes itself as "the world's first civil society intelligence agency", admit that their suggested countermeasures are "not foolproof".

"The technology of remote control warfare is impossible to control," the report says.

"The ultimate defence is to address the root drivers of the threat in the first place."