We have a handy guide to the cast of all seasons from 1 through to 5, for those wanting a recap before the new series lands. I think what is interesting about all three key guys is that none of them fitted the military mould of that era. Astonishingly, Stirling persuaded the high command in Cairo that he could achieve something significant at low cost in men and materials. Mortimer adds: “I interviewed three of the veterans who were on the operation and that’s exactly how they described it.

Through the writing I tried not to refer to other fiction, and tried where possible to refer to first hand accounts. This is a book for readers of second world war history who like the Boy’s Own version of the conflict.

Based on a book of the same name by Ben Macintyre, the show has caused a surge of interest in the founding members of the SAS and their lives outside of the regiment.

Also in the first episode, Stirling and Lewes take the plunge with their daring, first-of-its-kind parachute jump in the desert. What they put up with was unthinkably more distressing and traumatic than anything that us TV people were having to put up with. Both his legal and sporting careers were put on hold when the Second World War broke out, and he was posted away to fight. More rebels than soldiers, Stirling’s team are every bit as complicated, flawed and reckless as they are astonishingly brave and heroic. But it was just a propaganda tool before Stirling came along and made it real – so he reckons he invented the SAS, and that’s good enough for me.It’s about a bunch of rag tag fellas who took matters into their own hands because they felt that the controlling forces weren’t capable of doing it themselves. Other details and characters – such as Sofia Boutella’s French intelligence love interest – are entirely fabricated. One time in Paris – September ’44 – Paddy and I were invited to lunch with various people, mainly the French. Everyone speaks so highly of your energy on set - what is the atmosphere that you like to create during filming?