The Endeavour star says stepping back into the past to play young copper Morse has been a magical mystery tour.
This second series, which comes to an end tonight, follows the early 1960s days of the detective who went onto be the telly favourite played by John Thaw.
“When you come back to something there should be a confidence, but there isn’t,” Shaun told The Sunday Post. “I probably know this better than I know myself but that’s very little!
“Sometimes I think that was exactly what I intended and other days it’s far from the mark. Playing Morse isn’t really comfortable and it comes and goes.”
What is consistent is Shaun’s friendship with Roger Allam, who plays his seen-it-all old-school boss, DI Fred Thursday.
“Do we have a good bond? No, we never speak,” smiles Shaun. “I’m just joking. He’s a top man and I can’t imagine the show without him.
“I couldn’t have wished for anyone better to play him, he’s an incredible actor. But that goes for the rest of the cast, too.
“If there’s one thing I’ve been really proud of in this series it’s that we’ve become much more of an ensemble piece.
“Each character has had his own crack of the whip and we’ve get to see much more of them.”
Shaun, who dated Irish singer Andrea Corr for four years, is clearly passionate about young Morse.
But, never the easiest of interviews, he reminded of me asking him last year about TV bosses tying him up to a lucrative “golden handcuffs” deal to keep the series coming.
“Why do you keep coming at that angle? These are brilliant episodes and I’m really proud of them but we’ll just have to see about more.
“Listen, I’m really grateful for this. I don’t think I’m above this in any shape or form but I don’t want to get complacent.
“As soon as I start to entertain the thought of doing something for more than the immediate future, the creativity goes. And I’m not willing to do that.”
Shaun’s been ringing the changes in his upcoming film, War Book. He’s part of a starry cast including Sophie Okonedo and Ben Chaplin.
“It’s about a group of civil servants who get locked in a room to work out what to do in the event of a major national crisis,” adds Shaun.
“Because it’s all in the one room, it’s in the vein of 12 Angry Men and I think it’ll be really good.”
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