British special forces soldiers in Afghanistan allegedly murdered civilians and faked evidence to make the killings look justified, according to reports emerging from the United Kingdom.

The extraordinary allegations are contained in a number of recent media reports about the activities of the British Special Air Service (SAS) in Afghanistan over the past 10 years.

They also come soon after the ABC revealed a number of killings of Afghans by Australian special forces soldiers are being investigated by a secretive Defence inquiry.

A former British army officer, Captain Mike Martin, told the Sunday Times newspaper he had expressed severe misgivings about the intelligence used to target supposed Taliban figures, but was then barred from the meetings where the targets were identified as a result.

"They (the SAS) would go in and kill members of a family based on faulty intelligence. The next morning there would be people going, 'What was going on last night? You just murdered a whole family'," Captain Martin said.

"The special forces night raids set our campaign back massively because they killed so many of the wrong people.

"They acted on very poor intelligence even when they knew it was poor. Some of their missions were so tenuous they were targeting guys who poured tea for the Taliban commander 15 years ago."

Even more extraordinary are the admissions by an anonymous British soldier in the Daily Mail newspaper that he and fellow SAS members killed unarmed Afghans, then planted weapons on their bodies and falsified incident reports to cover up the circumstances.

The man claimed the tactics were justified because high-value Taliban targets were too clever to show hostile intent, and were often released after being captured.

"They wouldn't be seen waving rifles around. Similarly, they wouldn't make mobile phone calls. They would employ another Afghan to make them on their behalf because they knew we were listening to what they were saying," the man reportedly said.

"So when someone is that careful to cover their tracks, what do you do? Arresting them was pretty pointless because they would only be held for a few days before being released. So for me, the end justified the means."

An Australian special forces veteran has also told the ABC that Australian troops also openly discussed the use of "drop weapons" to make it look like Afghans had been armed when killed.

The anonymous British SAS member quoted by the Daily Mail said official battle reports were doctored to make it seem that Afghan Government forces had killed insurgents, but this was done because there was political pressure to make it look like the Afghan security forces were competent.

Do you know more? Please use this form to get in contact with the ABC Investigations team, or if you require more secure communication, please choose an option on the confidential tips page.

"So, yes, they were given undue credit for successful operations. You would then get generals and defence ministers boasting about how well the Afghan forces were doing, which used to make us laugh," he said.

"We knew how bad they were and we only took them along to 'put an Afghan face' on a mission."

The Sunday Times recently reported that a massive secret investigation by the Royal Military Police into allegations of war crimes by the British SAS had been scaled back, raising fears that the Ministry of Defence was seeking to cover-up war crimes in Afghanistan.

In Australia, the Inspector General of the Australian Defence Force is carrying out an inquiry into the broader culture of Australian special forces, but more specifically allegations of unlawful killings in Afghanistan.