Endeavour's Roger Allam on playing an alcoholic and his own boozy days

To that list Allam could add The Missing, Game of Thrones and Cabin Pressure or the Falstaff that won an Olivier award in 2011. And the full-faced, but in the flesh not in the least bit portly, actor’s turn as Inspector Javert in the original London production of Les Misérables remains unmatched, despite Russell Crowe’s best efforts.

Though Allam, sitting opposite me in a West End office, is niggled when I compare his low, expressive baritone to Roger Whittaker. “Roger Whittaker! I have not been listening to any Roger Whittaker whatsoever.” Still, singing or not, the thesis is simple – if Roger Allam is in something, then everyone likes it.

That thesis is about to be tested by the arrival of The Hippopotamus (in cinemas now), the film version of Stephen Fry’s acclaimed 1994 novel of the same name.

Allam plays Ted Wallace, a one-time poet and now piss-pot middle-aged theatre critic who is fired from his newspaper after a drunken altercation with the entire cast of a particularly bad Coriolanus. “It must be every critic’s dream,” Allam says, “when you’re at something utterly intolerable to actually get up and intervene and make it stop.”

Has Allam ever been on the receiving end? “Not people crying out in rage and disgust,’ he says. “There was quite a lot of cruelty around Michael Frayn’s play Afterlife at the National, and that was difficult. Michael hasn’t written another play partly because of that.”

Meanwhile in The Hippopotamus, Wallace finds himself at the country house of an old friend, whose sister he once had an affair with, attempting to discover what is behind the miraculous events his goddaughter claims to be happening there.

The plot teeters and threatens to fall apart but just about works whenever Allam is on screen. He gives the sort of gruff but decent Allam performance that has made his Detective Inspector Fred Thursday in ITV’s Morse spin-off Endeavour such a delight for us and, it turns out, for Allam.

“I’ve put more of my life, literally more of my time, into performing Thursday than I have done anything else,” he says. “One of the things that really attracted me about Fred Thursday is he was much more from the background of my family – my parents’ generation of my family, not me so much – than the characters I have often played: you know, sneering, upper middle class.”

Allam went to a rather grand school – Christ’s Hospital Sussex, “Eton for poor boys”, as he describes it. Is he a little sneering and upper middle himself? “Well, certainly not upper middle class, but I think I can access a sneer or two.”

He says Endeavour’s success is very welcome. “It addresses certain issues with my bank balance, and being an oldish father with youngish sons, that’s a comfort.”

Allam has two children with the actress Rebecca Saire: William, 17, and Thomas, 12. “Watching your children growing up makes you aware of time passing,” he says. “You think, ‘Oh, God, look at them now! He won’t be like this for much longer.’ Luckily, both my kids are very tactile, my youngest can still fit on my lap, but soon, very soon, that won’t happen any more.”

Allam is 63, has he worried about dying when his boys are still very young? “Yes, that’s it.” He says the sense of his own mortality arrived with a significant birthday. “Fifty is when it really kicked in, I suppose. That’s when you think, ‘Ah, right – let’s see.’”

How did he deal with those worries? “There’s nothing you can do about that really, except try and stay alive longer. It seems to be working so far.”

The boys are not Endeavour fans but they are, like any sentient human being who has heard it, very keen on Allam’s role as First Officer Douglas Richardson alongside Benedict Cumberbatch in Radio 4’s airline comedy Cabin Pressure, broadcast between 2008 and 2014.

“My two boys can quote it at me, you know… I get a lot of Douglas Richardson off them.” Richardson specialised in withering sarcasm. We get more of the same from Ted Wallace, though also big dollops of drunken anger.

Was Allam quite boozy himself? “Oh, yes! Yes, yes. Yes.” What, three-day benders? “Not quite that. But you know those nights when you get home and all there is left to drink is Dubonnet. Terrible. Dubonnet and a pork pie. Oh, God.”

Allam is almost constitutionally baleful, but he claims to have had wild days at the Royal Shakespeare Company. Drugs? “Not for me, no. Butt of red wine, really.”

In the RSC’s 1983 Romeo and Juliet he played Mercutio to Daniel Day-Lewis’s Romeo. Day-Lewis went on to become one of the most lauded actors in the world. Likewise his Cabin Pressure colleague Benedict Cumberbatch became a huge star.

Does Allam feel he has achieved all he could? “That’s the thing with acting,” he says. “There are always loads of people who are more successful, richer, more famous and seemingly able to do anything they want. I wasn’t particularly sharp-elbowed, I never said, ‘Right, I’m going to stop doing all this and I’m going to go to LA and see if I can make it out there.’”

Does he regret that? “I have my successes and I have children I love and enjoy being with. It doesn’t really get much better than that.”

The Hippopotamus is in cinemas now