Jack Lowden almost quit acting before he found mainstream success

He told The Sunday Times: "I just didn't want to do it anymore. I didn't feel like I fitted into the persona of an actor. There was me at 27 thinking about stopping because I felt self-conscious or like I didn't know how to do it."

But Jack then admitted that it was seeing Saoirse on set in the title role that "inspired" him to carry on.

He said: "And then watching this 23 year old [Saoirse carry the weight of a huge film like that with ease and grace and majesty. It was remarkable to watch. She makes it look so easy, like breathing. It was totally inspiring."

Jack plays up-and-coming MI5 agent River Cartwright in 'Slow Horses' - which is set in London and follows a department of intelligence agents - and felt instantly when he read the script that he could "pull [the character] quite close" to himself and has embraced the "cynical" aspect to his "incredibly sarcastic" alter-ego.

He said: "I saw really quickly when I read it that I could pull River quite close to me.

"He's quite miserable, he leans towards cynicism, like I do, and he's incredibly sarcastic. I've never leant very naturally towards the complete package. When I was growing up my hero was Norman Stanley Fletcher in the sitcom 'Porridge'. Ronnie Barker."