"It's all lying," Bill Nighy says. "It's one big elaborate lie. That's what's involved."
We're discussing the finer points of acting because, really, who better to ask? The veteran British actor has starred in everything from massive blockbusters to quiet indies, giant action spectaculars to understated romcoms and even animated features since starting out in the early '80s.
Since then he's won Golden Globes and Baftas and become an audience favourite, with his posh, gently cantankerous charisma. Indeed, when word leaked of my interview no fewer than three of my female colleagues made a special trip to my desk just to voice how envious they were.
"If you get past 50 and you're still broadly in one piece you do get asked 'the thinking woman's crumpet' question," he says with sly bemusement. "It's a difficult question to answer without giving the impression that you think you might be."
Nighy is in New Zealand to promote his new film,Their Finest, a dramedy set in London during the blitzkrieg of World War II, which opens in cinemas this Thursday.
"The first thing you should know about the film is that it's a cracking good night out," he says. "It's a film that's about big things but it never forgets to entertain. You get to laugh, you get to cry and it gives you something to think about it on your way home.
"That's not PR," he quickly adds. "That's just the way it operates. I've been all around the world with this film and that's how people respond."
He's not wrong. The film, which also stars Gemma Arterton and Richard E. Grant, is filled with delightfully funny moments but also doesn't shy away from depicting the brutal reality of life during wartime.
It follows a British film crew making a propaganda movie designed from the ground up to boost the nation's morale. In it Nighy portrays veteran actor Ambrose Hilliard.
"They were looking for someone to play a chronically self-absorbed pompous actor in his declining years and they came to me," he smiles. "It was a real stretch."
Despite his brutally self-deprecating humour the role wasn't entirely without challenge. Nighy was basically playing two roles; firstly as Hillard and then as Hillard acting as drunk Uncle Frank in the propaganda film.
"It was odd," he admits. "I've never done that before. But it was fun to not only get to play my part, the actor, but to also get to play the part that he's playing in the film we're making while you're watching the film. It was good value."
While we get to see Hillard's approach to acting in the movie, Nighy's preparation for the role was somewhat different.
"I've reached an age where I can answer certain questions entirely honestly without having to pay lip service to certain myths. How much research did I do for this film? Absolutely none whatsoever. Everything I need is in the script. You don't have to have lived anything to act it otherwise we wouldn't need actors. The whole thing would fall apart.
"If you needed to be divorced to act divorced it would be a very strange way to cast things. The fact that anyone's been divorced doesn't mean they can act it. Most people can't act being divorced because they can't act... contrary to popular opinion."
That last bit could sound a bit snippy. It's not. There's a lightness to his conversation, and he possesses a nimble and dry sense of humour.
"I like when comedy is buried, where it's disguised," he explains. "It's no less effective and it's certainly no less funny."
Despite his long list of movie credits Nighy's most beloved role remains that of grumpy old rocker Billy Mack in 2003's love-it-or-hate-it romantic comedy Love, Actually.
Just last month the star-studded ensemble cast reunited for a brief 10 minute micro-sequel to aid the UK charity Comic Relief. How did it feel to reacquaint himself with Mack?
"It was a bit of a shock to be honest. It was like, 'how do I play this?' I had to watch a bit which was not a good idea because I just thought, 'Oh my God, what were you thinking?' which is my response to anything I've done. But once we got going it was fine.
"The big news is that I can still get into those trousers, " he laughs. "So that was a relief."
Nighy on Nighy
On... Their Finest
"To young people World War II is ancient history but it's not that long ago that things were messed up. History is the most important thing. Even though people are always trying to rewrite it.
On... Shaun of the Dead
"I thought it was the funniest script I'd ever read. I told them [Simon Pegg and Edgar Wright] that and they didn't believe me because it was the first script they'd written."
On... how he chooses his films
"I like to present a moving target, try and do something different from what I've just done to shake it up a touch. I don't mind what genre it is or what the target audience is. As long as they're serious people with a good quality script. And obviously good people."
On... his dream role
"I like to keep a balance between straight roles and comedy things. I'd like to have superpowers... And I'd rather be a vampire than a wizard. They wear cooler clothes."