Drones guided by thought control raise the possibility of machines instead of men being blamed for military accidents and war crimes, a leading scientist warned on Tuesday.

Fast-moving advances in neuroscience mean that pilotless attack planes controlled by an operator's thoughts may be a reality in the "not too distant future", according to Professor Rod Flower.

But he warned that such technology would take ethical concerns over the use of drone weapons to a new level.

The CIA's use of drones to "take out" alleged al Qaeda terrorists in Pakistan, Afghanistan and elsewhere has already stirred up a storm of controversy, with claims of numerous innocent civilians being killed.

Prof Flower, a biochemist at the William Harvey Research Institute, Queen Mary, University of London, chaired a Royal Society working group looking at the potential military impact of advances in neuroscience.

In their report, one of a series from the Royal Society looking at the field of neuroscience, the experts call on the UK government to be as "transparent as possible" about research into military and law enforcement applications.

They also urge scientists to be aware that their work could be used to harm as well as help and heal.

One such area of cutting edge research involves the development of "mind-control" systems to aid people severely disabled by illness or injury.

Scientists have already demonstrated how a patient's thoughts can be used to move prosthetic limbs or a cursor on a computer screen.

Prof Flower said it may not be long before thought control technology is applied to military machines.

At the same time, drones were becoming increasingly autonomous, raising serious ethical questions.

Speaking at a press conference in London, Prof Flower said: "At the moment, drone control is like controlling a model aircraft, but supposing some time in the not too distant future a drone was controlled by your thoughts.

"The drone may even have some self defence capability. You could see a situation where what you think and what the drone interprets you thinking is very, very blurred. So where does the responsibility for blowing up a wedding party lie? Is it with your brain or the software in the drone?"

The working party focused mainly on chemical weapons designed to incapacitate temporarily rather than kill.

Scientific evidence suggested it would not be possible in the foreseeable future to develop a "safe" incapacitating agent.

The death of more than 100 hostages in 2002 after Russian forces used a knock-out gas to storm a theatre seized by Chechen terrorists showed how the use of such weapons can go disastrously wrong.

Yet there were worrying indications of moves to develop incapacitating chemicals for use in domestic law enforcement and riot control, said the working group.

Although the Chemical Weapons Convention (CWC), which the UK has signed, forbids the military use of incapacitating agents, it permits their use for "law enforcement including domestic riot control purposes".

In 2009 the British Government issued a statement suggesting that employing such agents for law enforcement could comply with CWC. Previously it had seemed to accept that CS gas and other "riot control agents" were the only chemicals permissible for law enforcement.

The working group urged the government to publish a new statement clarifying its position.

Prof Flower said: "We know that neuroscience research has the potential to deliver great social benefit - researchers come closer every day to finding effective treatments for diseases and disorders such as Parkinson's, depression, schizophrenia, epilepsy and addiction. However, understanding of the brain and human behaviour coupled with developments in drug delivery also highlight ways of degrading human performance that could possibly be used in new weapons, especially incapacitating chemical agents.

"This is why it is so important that the UK government is clear about its reasons for the changes made to its interpretation of the law enforcement exemption in the CWC."