As one of the safest pairs of hands in Hollywood, Gary Oldman isn't the kind of actor you imagine being overwhelmed by any role. If you can do Churchill and win an Oscar while you're at it, then you're basically bulletproof, right?

However, the actor has revealed that pressure he put on himself while preparing to play George Smiley in Tinker Tailor Soldier Spy - following in the footsteps of Sir Alec Guinness - pushed him to the brink of mental collapse.

"I had let it get to a point where it was going to crush me. It almost gave me a bloody nervous breakdown, I was so caught up in the fear of this," Oldman told an audience at his Cannes masterclass Q&A.

Fortunately, his nerves settled. "I did the first scene, and once I had opened my mouth and started doing it, I realised, ‘I know where I am. I’m on a set and I’m acting.'"

Throughout the Q&A, Oldman gave a fairly downbeat assessment of his past hits and performances (Sid & Nancy: "I don't think I'm very good in it; Dracula: "pretty good") and despite the strain of playing Smiley, insisted that "insecurity is a good thing".

"I think it will be a sad day to be able to watch yourself and say, ‘I think I’m fantastic in this'. Having doubt and insecurity is a good thing, but you can’t let it paralyse you," he said.

He also spoke about his breakout role in Sid & Nancy, initially dismissing it as "a lot of noise" before deciding to commit to it: "I lost a ton of weight and made myself very ill.”

Oldman then chatted about working with an opera singer to lower his voice by an octave to play Dracula in Francis Ford Coppola's Bram Stoker's Dracula.

"He’d been a hero of mine. I thought Coppola might be able to do something very interesting with it. And ‘I’ve crossed oceans of time to find you’ – I thought, 'It’s worth doing the movie just to say that line.'"

Finally, he turned to what keeps him interested in acting.

"Churchill was going to take every molecule of my being to pull off. But you look for other stimulus," Oldman said.

"You can’t always sit around and wait for that great role to come along. You’ve got to work and you’re not always going to be hitting home runs."