British special forces have committed a series of murders in Afghanistan, the BBC reported.

Recent military reports suggest that one unit may have illegally killed 54 people in six months.

The BBC understands that General Sir Mark Carleton-Smith, the former head of Britain's Special Forces, was informed of the alleged illegal killings but did not hand over evidence to the Royal Military Police even after the investigation was launched.

BBC Panorama has reviewed hundreds of pages of SAS operational reports, including reports of more than a dozen raids by a SAS squadron in Helmand in 2010/11.

Individuals who served with the SAS squadron on that deployment told the BBC they witnessed the SAS operatives kill unarmed people during night raids.

They also said they saw the operatives using so-called "drop weapons" - AK-47s planted at a scene to justify the killing of an unarmed person.

Several people who have served in special forces said SAS squadrons compete with each other to commit the most murders. Internal emails show that officers at the highest levels of the Special Forces were aware of possible illegal killings but did not report suspicions to military police, despite a legal obligation to do so.

The Defense Department said it could not comment on specific allegations, but the refusal to comment should not be taken as an admission of the factual accuracy of the allegations.

A MOD spokesperson said that British forces "served with courage and professionalism" in Afghanistan and were held to the "highest standards".