'Younger people don't know what it's like being old... life carries on with just the same passions, excitement and fun'
Sir Ian McKellen and Dame Helen Mirren unite for the first time on screen in The Good Liar, in which they play a conman and his mark. The pair sit down with Laura Harding to explain what took so long
Sir Ian McKellen and Dame Helen Mirren are seated side by side in comfy-looking armchairs, sipping from delicate china cups and talking animatedly.
You get the feeling that if you walked into the room two hours earlier or two hours later, you would find the same scene.
The pair swap gossip and war stories and laugh uproariously.
The fact they are such good mates makes it all the more surprising they have not appeared on screen together until now, in the new thriller The Good Liar.
What can possibly have taken so long?
"It's a very good point," Dame Helen (74) acknowledges, smiling. "I would ask the same question actually."
"You often don't work with people who you long to work with," Sir Ian (80) adds. " People who you know you get on with and act in the same way.
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"We both have our background at the Royal Shakespeare Company and then we have both been lucky in movies as well, so you would think it would be natural."
They are tickled that their union is such an event that posters for the film bear only their surnames, as if they were action stars.
"You end up this curious star called Mirren McKellen," Sir Ian jokes. "My God, I want to meet him or her."
The pair have worked together on stage in Strindberg's Dance Of Death on Broadway, but it is remarkable that they have never found themselves on the same film set.
"Life doesn't necessarily take you in that direction," Dame Helen says.
"But here we were very lucky that a brilliant director called Bill Condon thought it would be good to put us together.
"We both signed up with alacrity and great pleasure.
"We've obviously known each other for a long time. We've done theatre together... we've led parallel lives."
Sir Ian interjects: "And we are neighbours. I often walk Helen's dog for her. She's never out of my pub (he owns The Grapes in London's Limehouse), are you?"
Dame Helen laughs uproariously. "He's such a liar."
Which brings us neatly on to the subject of their on-screen union, The Good Liar, in which Sir Ian plays conman Roy Courtnay, who sets his sights on the recently widowed Betty McLeish and plans to take her for everything she has.
It's by no means the first time the actor has played a character with a villainous streak - he's depicted pretty much every Shakespeare baddie going - but this does mark a change in his on-screen roles after becoming so beloved for playing Gandalf in the Lord of the Rings film and Magneto in X-Men.
"The devil has the best tunes," he says.
"Often, the best part in the movie is the villain. Why? I don't know. Maybe an audience is intrigued by what is true and what is not. At a distance, you can be thrilled by really nasty goings-on, so they are good characters.
"That Roy is a conman is rapidly obvious, but who he actually is, where he comes from and what his motives are... that's part of the fun of watching the story unwind. His moustache is real, I'll tell you that much.
"It's actually very difficult to write a really interesting good character... Jesus, I suppose."
Dame Helen nods and says: "Even with Jesus, it's maybe his flaws that might make him interesting because it is your flaws and vulnerabilities that make you an interesting character. That is what we are always looking for as actors."
It's also conspicuous that this is a film about two people in, dare we say it, the later years of their lives. A story about a relationship between older characters is hard to come by, especially one that does not revolve around death or fatal illness.
"Younger people don't know what it's like being old," Sir Ian says.
"I am 80 and this year I went to a reunion of my form from school. There were 30 of us and 10 didn't turn up because they were dead, incapacitated or didn't want to come.
"The other 20 are hale and hearty, retired long ago, full of beans. They couldn't wait for the next party.
"I think that is the norm now for 80-year-olds, as much as people are incapacitated, but young people tend to run the world."
Dame Helen chimes in: "They don't realise that life carries on and it does, if you're lucky and, as Ian says, healthy and active in life.
"Life absolutely carries on in the same ways, with just the same passions, the same excitement, the same fun."
But there is one thing that is a bridge too far for Sir Ian now he's old enough to pick and choose what he cares about.
"I did think the other day, as we battle through Brexit, I thought, 'Oh good God, when I'm long dead they still won't have the Brexit deal complete'.
"I won't take a view on it and I've withdrawn entirely, emotionally, from the race and am watching it as a bit of chess.
"All I can say is, they are wretched players and don't know a pawn from a queen."
The Good Liar is in cinemas now