The Special Air Service (SAS) is a special forces unit of the British Army. The SAS was founded in 1941 as a regiment and later reconstituted as a corps in 1950. The unit undertakes a number of roles including covert reconnaissance, counter-terrorism, direct action, hostage rescue and human intelligence gathering. The corps presently comprises 22 Special Air Service Regiment, the regular component, under the operational command of United Kingdom Special Forces, and 21 (Artists) Special Air Service Regiment (Reserve) and 23 Special Air Service Regiment (Reserve), which are reserve units under the operational command of 1st Intelligence, Surveillance and Reconnaissance Brigade.

A former head of Britain’s Special Forces has challenged Theresa May’s claim that President Assad was behind the chemical attack in Douma.

Major General Jonathan Shaw said: ‘Why would Assad use chemical weapons at this time? He’s won the war.

‘That’s not just my opinion, it is shared by senior commanders in the US military. There is no rationale behind Assad’s involvement whatsoever.

‘He’s convinced the rebels to leave occupied areas in buses. He’s gained their territory. So why would he be bothering gassing them?

Speaking exclusively to The Mail on Sunday, the ex-SAS and Parachute Regiment commander added: ‘The jihadists and the various opposition groups who’ve been fighting against Assad have much greater motivation to launch a chemical weapons attack and make it look like Assad was responsible.

‘Their motivation being that they want to keep the Americans involved in the war – following Trump saying the US was going to leave Syria for other people to sort out.’

His views were echoed by Admiral Lord West, former head of the Royal Navy, who said: ‘If I was advising President Assad, why would I say use chemical weapons at this point? It doesn’t make any sense. But for the jihadist opposition groups I can see why they would.

‘But one must give Theresa May the benefit of the doubt and trust she has seen some unequivocal evidence which leaves no doubt that Assad was behind the atrocity.’

But the ex-commander of the Army’s chemical weapons regiment, Colonel Hamish de Bretton-Gordon, said: ‘A sophisticated nerve agent was used at Douma, not just chlorine. Only Assad has the capability to produce these substances inside Syria. And using chemical weapons is his standard modus operandi.’