With a trademark gentle smile, Jim Broadbent is considering what life advice he’d give his younger self.

“I’d say, ‘Give yourself some slack. You’ve got to be in it for a long time, don’t be too impatient’.”

The much-loved actor is speaking with the benefit of hindsight, of course (and an impressive awards cabinet – including an Oscar, for 2001 film Iris). But what would 21-year-old Broadbent make of the glittering career that lay ahead?

“He would be delighted,” says the actor, now 67, with a laugh. “[He’d say] ‘God, he’s still doing it!’”

Broadbent explores the themes of youth, ageing, and looking back in his new film, The Sense Of An Ending, based on the Man Booker Prize-winning Julian Barnes novel.

He plays divorced, retired and not always likeable Tony, who is forced to revisit his past when the mother of an old university girlfriend leaves him a mysterious diary in her will.

The diary is now in the possession of his frosty ex, Veronica (played brilliantly by Charlotte Rampling), however, and much to Tony’s frustration, she won’t part with it.

As he embarks on a mission to retrieve it, he delves deeper into his youth – where we see flashbacks of a younger Tony and Veronica, played by Billy Howle and Freya Mavor – and discovers that not everything is as he remembers it.

His behaviour towards Veronica, for one thing, wasn’t as understanding as he’d recalled it.

It’s a thought-provoking film, and Broadbent admits it prompted him to ponder his own younger years.

“Inevitably it throws up lots of questions – memories of your school days, student days, and behaviour and friends,” says the Lincolnshire-born actor, who insists there were “no great revelations” when he looked back.

“Life’s like that anyway; you’re always thinking back, just remembering things,” he adds.

“It’s interesting thinking about how flawed your memory is as well, and slightly questioning what you have always assumed is your past. [Thinking], ‘Maybe that wasn’t quite as clear cut as I remember...’”

Tony shares his memories, and progress updates for the diary hunt, with his ex-wife Margaret (Harriet Walter), who often finds herself exasperated by his self-absorption.

“They are divorced, so clearly there were tensions and regrets within their past and, to some extent, they’re still there,” says Broadbent, who is married to painter Anastasia Lewis.

“But they were married for years and years and they do have an awful lot in common, so the relationship reaches a plateau where they can work together to some extent.”

The pair have a daughter, Susie, who is pregnant after opting to have a child on her own through IVF.

In the absence of a partner, it falls to Tony to join Susie (played by former Downton Abbey star Michelle Dockery) at birth preparation classes – which is where the rather selfish, grumpy character gets to show his kinder, more loving side.

“It was awkward, as I’d only just got to know Jim; I’m bending over a big bouncy ball and he’s sat behind me massaging my hips,” Dockery recalls of the antenatal scene.

“It was so weird and appropriately awkward for the scene because, of course, she’s with her father and everyone else in the class were real couples.”

“It was a nice way to film it,” Broadbent says. “Certainly, the intimacy that was required between a father and daughter seemed quite real in its awkwardness, I suppose.”

In real life, Broadbent has a quiet, unassuming presence and is, as the film’s director Ritesh Batra notes, “a little shy”.

He admits he took pleasure in playing a character so curmudgeonly he’s been nicknamed ‘Mudge’ by his daughter and ex-wife.

“I enjoyed that, because I’ve been playing quite a lot of Father Christmases recently, who’s the least curmudgeonly person,” he says, referring to his roles in Arthur Christmas (2011) and Get Santa (2014).

“It’s quite nice, occasionally. I have played Scrooge [in a West End version of Charles Dickens’ A Christmas Carol], but he ends up nice.”

Next up for the actor is a role in the seventh series of fantasy TV phenomenon Game Of Thrones - a very different beast to the understated The Sense Of An Ending.

“Five visits to Belfast [where GoT is filmed], and each one I just came away in awe of the production. How this juggernaut has been managed, of high creative art, with such expectation, is wonderful,” Broadbent says, eyes widening.

“The producers are sensational, how they keep it all moving to such a high level. I don’t know how they do it. So I’m thrilled to be part of it.”

He’s not giving much away about his character, however.

The Sense Of An Ending has been in cinemas since Friday, April 14.