IT’S the sort of invitation, military historian Damien Lewis describes, as a once in a lifetime opportunity. About ten years ago, the bestselling author received a call from an amateur historian, Peter Forbes, in Northern Ireland. Forbes told him of the existence of a treasure trove of files about the Second World War origins of the SAS: the family of one of its main protagonists, Lieutenant Colonel Blair ‘Paddy’ Mayne, had kept the files hidden for many years. Would Lewis now like to see them?

The result is Lewis’ latest book: SAS Brothers In Arms draws on this previously untapped archive of material to tell the story of how a group of ‘rough diamonds’ answered Churchill’s call for volunteers for Special Service, going deep behind enemy lines in North Africa to play their vital part in the earliest Allied victories. The activity of the fledgling SAS was not just a turning point in the war: it was also a new way of fighting for the British Army. While the top brass were initially suspicious of the SAS, disbanding it after the Second World War, it soon returned to become one of the most feared units at the British Army’s disposal.

With characters such as Paddy Mayne and David Stirling, it’s easy to see why this is a tale that has captured the imagination. Their North African adventures are also currently the subject of a BBC drama series, SAS: Rogue Heroes, starring Connor Swindells and Jack O’Connell. Lewis diplomatically told me he had been too busy doing the book publicity to watch the programme as yet, but I’ll say that if you’ve enjoyed that dramatisation, then this book gives you the history in much richer detail.

Damien Lewis is one of those non-fiction writers who brings his scenes brilliantly to life. When I asked how he achieved this, he ascribed it to his previous career as a war correspondent – he can tap into that experience of time embedded on the frontline. He also described two journeys driving across the Sahara, and the fear and terror that comes through getting lost in the middle of the desert.

As well as his history writing, Lewis has also written extensively on more recent military exploits. Does the original SAS philosophy linger on today, I wondered? Lewis recalled working with Des Powell on Brave Three Zero, about one of the SAS units who went undercover in Iraq during the first Gulf War, in search of Saddam’s Scud missiles. The vehicles and weapons were ‘slightly better’, Lewis noted, but otherwise, the ethos and the exploits in the deserts were pretty much the same.

Damien Lewis is appearing at Waterstones Salisbury on Thursday, November 17, 7pm.