Sir Ian McKellen is a larger than life presence. Sitting across from him at a large round table in a hotel suite room, it occasionally feels like we're having a relaxed chinwag at Bilbo Baggins shire cottage. He sets a genial atmosphere, booming with laughter and radiating wisdom. For his latest film he's teamed up once again with director Bill Condon (Gods and Monsters, Mr Holmes) who has adapted Nicholas Searle's novel The Good Liar. It is, however, the first time he has worked on a film with Dame Helen Mirren who plays a wealthy widow. McKellen's conman meets her online and sets up a scheme to steal her money. 'Have you seen the film?', he enquires when asked to comment on his scenes with Mirren. 'That's more than I have!' he laughs.

On working with Mirren on a film, McKellen says, 'It was like I thought it would be. It was jolly good fun!' And on the reasons he continues to work with Condon he chirpily explains, 'Bill always treads a wonderful atmosphere, whether it's a big film or a small film. He's always in charge, but always excited to be there as if he's at someone else's party, rather than the one he's organised. When it comes to Bill I have total confidence. You know it's going to be brilliantly lit and photographed, you know the costumes are going to be fantastic. You know the whole production around him will be great, you know it will be very well cast. What's to complain about?'

credit: Chiabella James

As you may have guessed from the title, the film is packed full of deception and intrigue and the question of whether actors are better liars than most comes up. His response is to break into Shakespeare, roaring, 'All the world's a stage, all the men and women are merely players! When we get up in the morning we decide as human beings what costume we're going to wear. You dress appropriately for the occasion. So, it will be this side of me on display now and if you're going out somewhere in the evening with friends, you'll take a whole other costume with you perhaps to change into. We're all actors so we only do what everybody else does all the time, which is why actors are fascinating to people because they can see we're not that different. Just a bit more adept at times.'

McKellen is currently celebrating his 80th year with a West End one-man stage show that recalls seminal moments from his life and career. On the reasons why he continues to keep working and why he loves his profession he says, 'I never assumed I would have success as a young person … that came in with The Beatles. I've always thought of it in terms of a career so to imagine a career would come to an end when it's actually been so interwoven into life, I can't imagine it! It will happen. The knees will give way, the lungs will give way, the mind will give way. I think that's why I keep going because it would be a pity when you get to that decrepitude and you look back and think I could've done that!'

The Good Liar is in cinemas from Fri 8 Nov.