However, it's rather ironic, given that theatre is his acting love, and he's set to return to Glasgow's Theatre Royal in the crime thriller, Rough Justice.

"I'm not a theatre-goer," admits the Paisley-born actor, speaking from his Hampstead home. "The sad truth is that so much of it is rubbish. And so much these days is dominated by some really dreadful musicals. So I just don't go."

Conti was last in town in Eric Chappell's comedy, Wife After Death, which, despite being very good, appears to have, well, died a death.

"It's a real shame," he says. "A few years back, Wife After Death would have run in London for three years. But when you're up against musicals ..."

His voice trails off then he adds wistfully: "But when theatre does work, it's really great."

The 70-year-old believes the Rough Justice script, written by Terence Frisby, to be a great piece of writing.

"I read it from start to finish," he says. "There are no dull bits. And Glasgow will like it. They're an intelligent audience and like to think a bit. And this play poses some big questions."

Conti will play television journalist James Highwood , who has made a career out of challenging the British justice system. Now, suddenly, he finds the system challenging him as he is charged with murder. He admits the killing – but chooses to defend himself.

"It's a highly emotional play," says the actor, "with a man pleading to manslaughter of a most unusual kind.

"And it's an examination of the law, about whether or not it's fair. And, of course, what is 'fair' in a court is of no interest."

Frisby once had to defend himself in court, and used his experience to write Rough Justice. And Conti, like the playwright, believes the law should be continually questioned.

"It should always be under debate," he says in a serious voice. "And, yes, subjects such as euthanasia should be weighed up. All of our laws are based on a Judeo-Christian background, and of course atheism is on the rise.

"So you have to put God aside and think more of Man."

Does he believe lawyers to be a necessary evil? "They are not always evil," he says, laughing.

"I know some splendid chaps who are judges, who are very liberal and very fair.

"Indeed, the bar enjoys a very liberal tradition. It doesn't mean they will always be fair in court but at least they do have liberal thoughts in their minds.

"It often goes wrong when politics crosses into the law. There are judges who can be relied upon to 'do the right thing'. And so they will be appointed to a certain case." And consider wars in Iraq to be legal? "Indeed," Conti says.

Does the Scottish system of 'not proven' come under question?

"Oh yes," he says, emphatically. "The result that says 'we're letting you off but don't do it again.' Yes, it's a cop-out."

Courtroom dramas are fascinating if well made, but, if not, they can be torturous.

"The actors playing the prosecuting council and myself sat through some trials at the Old Bailey and we realised that, if this were real theatre, the audience would have left before the interval.

"It was all so tedious. There are moments of cross-examination when it brightens up, but for the most part nothing happens – lots of shuffling of papers and looking up books, and you can have five-minute periods of silence."

So how does the play hold an audience?

"Well, the story sustains," he says. "It grabs the audience right from the word 'go'.

"There is no preamble, you're right into the drama with the first line of the play, and then you go with the twists and turns."

Touring theatre combines with Conti's film career: he appears in the latest Batman movie, The Dark Knight Rises.

"The contrast makes life interesting, I suppose, but acting in the theatre is really more fun," he says. "I love the contact with the audience.

"And doing a movie means waiting about for so long. You spend hours every day doing nothing."

Conti adds: "I'm writing a novel at the moment but you can't write in between shooting. It just doesn't work. And then there comes a time when you just can't stand that any more."

Yet Rough Justice is demanding. "Oh, it certainly is. The learning process of the lines was just enormous.

"And what made it harder was the form of the language. Court speak is not naturalistic, so it was very hard to learn."

But he's looking forward to returning home.

"It's always a treat to come back," he says. "And in some ways, with a drama, it's a relief not to be funny.

"Plus, I get to go to Rogano, a restaurant which hasn't changed since my parents took me there as a boy.

"Perfect."

n Rough Justice, Theatre Royal, August 29-September 1.