IAN McDiarmid is the most reluctant of Hollywood stars. A more flighty actor would have taken offence when, at the red-carpet premiere of Star Wars: The Phantom Menace in 1999, none of the photographers knew who he was.
But the Carnoustie-born psychology graduate laughed at the oversight. He couldn't blame them given that he was not wearing the prosthetic make-up that had transformed him into the dark lord Emperor Palpatine in 1983's Return Of The Jedi, and, in any case, McDiarmid revelled in his anonymity.
"I went with a friend who's not in showbusiness, and they'd shout: 'Who are you?' and make remarks about her clothes as we walked down," he says. "It's just abuse, that's all it is. I thought: 'Thank God they don't know who I really am,' but then the producer told me not to be ridiculous and dragged me over to CNN and said: 'This is the Phantom Menace!'"
Until that point, McDiarmid had enjoyed plenty of success, just on a more modest scale. Having cut his teeth at Glasgow's Citizens' Theatre in the early 1970s, he went on to take leading roles in Manchester, London and with the RSC. He was voted most promising performer by the London Theatre Critics in 1977, and a few years later won the then Society of West End Theatre's Award for best actor for his performance as Einstein in Terry Johnson's Insignificance. It was thanks to playing an elderly Howard Hughes-type character in Sam Shepard's Seduced at the Royal Court that he was considered for the part of the 120-year-old Palpatine in Return Of The Jedi.
In 1990, he and fellow actor Jonathan Kent took on the directorship of Islington's 300-seat Almeida Theatre, establishing it as the fringe venue every A-list star wanted on their CV. During their 13-year reign, they attracted performers of the calibre of Kevin Spacey, Juliette Binoche and Ralph Fiennes, and picked up a set of rave reviews to match. One critic called it "a centre of enlightened internationalism".
It all sounds terribly glamorous, but McDiarmid was in it for the joy of acting. That's why, after playing the younger Palpatine in the three Star Wars prequels, he chose a role in a West End play rather than trying to pursue a Hollywood career. The reviews for his performance in Brian Friel's Faith Healer were duly ecstatic ("One of the finest things on the London stage," said the Guardian), but it was only when the production transferred to Broadway that McDiarmid appreciated the full measure of what his Star Wars fame actually meant.
"As it went on, I became much more recognisable and everybody then wanted an autograph and sometimes a bit of you," says the 64-year-old, sitting in his furnished dressing room in London's Gielgud Theatre as the acclaimed run of Luigi Pirandello's Six Characters In Search Of An Author comes to an end. "When I went to New York with Faith Healer there were large groups of people at the stage door when we were rehearsing. I thought they were there for Ralph Fiennes, but they were Star Wars fans. I started to sign things, and one of the producers said he wished I hadn't because it's an industry and it would be all over the internet, as indeed it was. So I told them I had a policy that I would only sign stuff to do with Faith Healer. That's when it turned nasty. They worked out who my driver was, followed me to my hotel, and when I said I wouldn't be signing anything, they did get quite heavy."
It was a troubling glimpse into the lives of those who find themselves hounded by the press and public, a subject figuring large in McDiarmid's imagination today as he stars in his own adaptation of Andrew O'Hagan's Be Near Me for the National Theatre of Scotland. Longlisted for the Man Booker Prize, the 2006 novel is about a Catholic priest, David Anderton, who takes on the fictional Ayrshire parish of Dalgarnock, where he develops an unhealthy obsession with the town's disaffected youth. After a night of hedonistic excess in which alcohol and repressed homosexuality get the better of him, the clergyman is prosecuted for sexual assault.
The reaction of townsfolk and tabloids is duly hysterical, but O'Hagan's purpose is more subtle. Although he portrays Father David as a flawed character – aloof, snobbish and self-absorbed – he makes it hard for the reader to regard the priest's misdemeanours as criminal, certainly not in the black-and-white terms presented by the red-tops. "O'Hagan explodes the clich," he says. "The community is looking for something to latch on to and chooses this inadequate priest, and they go for him. That gives them a feeling of unity and a sense of purpose."
It was this conflict between a man and his society that inspired McDiarmid to adapt the book for the stage. Like David Harrower's globally successful Blackbird, which is about the sexual relationship between a grown man and an underage girl, it dares to acknowledge the ambiguity in a situation we would prefer to regard as clear-cut.
"At its heart it's about the uncomfortable and disquieting nature of love," says McDiarmid, an atheist of Presbyterian stock. "The character is foolish to have taken the job – how's it going to turn out well? He is adrift and in exile from himself, an accident waiting to happen. His religion is an escape from life."
Although Father David's behaviour is professionally hypocritical and socially foolish, the community is wrong to label him a pervert. "He kisses a 15-year-old boy once," says McDiarmid. "He shouldn't have done it, but he isn't a paedophile. That's part of what the book deals with: the need for people to put others into pigeonholes in order to deal with them."
He says it is just a weird coincidence that only last year in Manchester he played a lonely clergyman who develops a friendship with a younger man in Robert Holman's Jonah And Otto. A more auspicious twist of fate was that NTS director John Tiffany was a fan of Be Near Me long before McDiarmid handed over his script. In fact, Tiffany had had lunch with O'Hagan only a couple of days before meeting McDiarmid and had named Be Near Me as his book of the year in a daily newspaper. "That's when I rather gingerly took out the script from my bag in a brown envelope," he says. "He looked astonished and a very few days later he said he wanted to do it. I'm still a bit heady about it."
Thus it is that McDiarmid will take to the stage of the Palace Theatre in Kilmarnock, the novel's home patch, before a major UK tour that takes in the Donmar in London, Edinburgh, Glasgow, Inverness and Perth. Also in the company is Taggart's Blythe Duff and Scottish stage favourites Jimmy Chisholm, Kathryn Howden and Benny Young. It is McDiarmid's first adaptation, and it could be his last, but he was determined the part of Father David had to be his.
"I wrote it as the actor who was going to play it," says the performer who last appeared on a Scottish stage in 1997 in John Byrne's Almeida adaptation of The Government Inspector. "I wasn't going to let anybody else do it! Knowing that I was going to act it, I could have certain things in mind subtextually that might be suggested by the character. The narrator figure has gone completely and you'll find out the story through the people in the community. He's written so many other powerful characters, not least his housekeeper Mrs Poole, whom Blythe Duff is going to play."
Next for McDiarmid is the role of Denis Thatcher in BBC2 drama Margaret, with Lindsay Duncan playing the Tory prime minister in her final days in office. "I suppose they saw how I could look like him," says McDiarmid, who has a similarly high forehead and receding grey hair. "It's extremely interesting about the nature of power. It's Roman: they're all out to stick the knives in her back, while Denis is holding the emotional fort at home, the perfect consort who never put a foot wrong."
• Be Near Me, Palace Theatre, Kilmarnock (01563 554 900), January 14–17 and on tour, www.nationaltheatrescotland.com