Off Colin Firth goes, darting around topics as unexpected as taking drugs, screwing up at school and flawed parenting. It’s odd for such a famous actor to be so candid, and even odder to find a star better looking off screen than he is on – old-school rugged, softly spoken and mahogany-brown after filming the big-screen version of Mamma Mia! in Greece. The 47-year-old actor didn’t like Abba: “Like most boys it wasn’t my thing. I was 14 in 1974 and fancied girls to death.”

Firth’s confessional mood echoes his role as Blake Morrison in the film version of Morrison’s autobiographical memoir And When Did You Last See Your Father?, which evoked the relationship between Morrison and his domineering father, Arthur. In this moving, quietly powerful film Firth and Jim Broadbent, as Arthur, have just the right kind of double-edged intimacy.

Arthur couldn’t be more different from Firth’s “quiet, unassuming” father. “But I was a surly, pretentious adolescent, like Blake’s portrait of himself. My father and I were not close in a cosy sense but I am as connected with my father as Blake was with his. The difference is my animosity with my dad was left behind in my teens. But, even now, three seconds in my parents’ company and a tone of voice or trigger will bring me back to being 15.”

Firth was born in Hampshire, then moved to Nigeria where his father taught. His parents have always been “eternal students” and it is a close family, he says. Firth lost his first grandparent (his grandfather, whom he was close to) at 35. “It was a shock,” he says, “some part of me finding out we weren’t immortal in my family.”

The family returned to the UK when he was small and Firth struggled to fit in schools in Bath and Essex. “Accents were an issue,” he recalls, grimacing. “It was a shock to hear aitches being dropped. I felt like a freak speaking with the accent I had. So I changed it and only started to speak like this when I was in the sixth form.”

He lived in America for a year when he was 12. “I feel quite strongly about antiAmericanism. I share people’s grievances about the current Administration but I remember my father and I watching the Watergate hearings. Here was a country arraigning its own leaders. America has a fantastic history of dissent.”

Something went awry in Firth’s teenage years. “I loathed authority but was frightened of it. My rebellions were sneaky, passive. I didn’t smash windows or get into fights – if I did I was strictly on the receiving end. Like Blake, I took refuge in books with the hope of getting laid by name-checking Dostoevsky. It wasn’t Hardy or Austen for me, but Camus. I grew my hair long, pierced my ears and then got slightly stranded by the punk thing.”

He loved music and joined “a not terribly good band” doing Doors covers. (A Gram Parsons fan, he nevertheless vociferously denies being a “dad rock nostalgic” and name-checks Wilco and Lambchop.) He also started to write, although “there comes a point,” he says gently, “when unless you practise something you have to classify it as a fantasy, but I do think there are worse writers than me who have published novels.” (Acting and writing are linked “because I quite like to do what I do to hide – by obscuring yourself you can reveal something”.)

Firth Sr could cope with the long hair but not Firth’s “bad choice” of friends. There was a charismatic hard nut at school who led Firth astray. Or “the misdemeanours that go along with wanting to be rock-and-roll and hippy, the music festivals, staying out late.” Drinking? “I was a bit naughty in that respect,” he says. Drugs? Firth looks stricken. “I’m not at liberty to go into detail about such misdemeanours. Yeah, it was all the usual stuff. If Labour Cabinet ministers can confess to some of those things, I probably can as well.” How did your father find out about the drugs? Did you smoke cannabis at home? “Nahhhuhhhh,” Firth mutters. “It was a whole series of things and was as much as to do with what he suspected. It wasn’t one incident.” The worst rows with his father “were about washing dishes and homework. There wasn’t a massive meltdown,” he insists.

But his teenage rebellion was concerted. “I would have gone to university had I not allowed myself to be derailed into moody adolescent laziness. I liked to characterise it then as a defiant decision to resist the system. But I was just resistant to schoolwork. If someone wanted me to read Shakespeare, I wanted to read Thomas Mann. If someone tried to make me listen to Brahms, I had to listen to Hendrix.” On the morning of A-level retakes, “I thought, ‘F*** it’ and went back to bed, it felt like a treadmill I didn’t want to be on.” Firth pitched up, “like Dick Whittington”, in London wanting to act and he got a job at a theatre switchboard. He read Kafka in his cubbyhole, and “stared into the abyss”, until he met a casting director who smoothed his way into drama school and then to a part in Julian Mitchell’s Another Country.

Sudden fame “blew me away”. He didn’t get on with his co-star Rupert Everett though denies all reports of 20-plus years of simmering rivalry and resentment. “Rupert got on with very few people. He found us all ghastly, naive and bourgeois. I envied his confidence. I was intermittently flamboyant but felt outside [and he puts on an LA twang] my comfort zone.” They have worked “very happily” since on The Importance of Being Earnest and – coming in December – St Trinian’s.

His looks and upper-class, ruffled demeanour meant he graduated from playing posh schoolboys to posh older men. There were appearances in A Month in the Countryand a controversial Falklands drama, Tumbledown. But Firth’s life really changed when he emerged, sodden-shirted, from the lake as Mr Darcy in the BBC’s 1995 adaptation of Pride and Prejudice. The screenwriter Andrew Davies recently revealed the plan had been for Darcy to be naked. Firth had “a bit of the usual tension about getting your kit off” but thinks it remained sexy because we “rerobed, not disrobed, Austen”.

He groans at the very mention of Darcy, whom he regards as “a part-time burden. It got my name recognised but it also put me in a box. Things were going well; I was building a diverse working life.”

Darcy made him feel “a bit of a star” (he smiles pleasurably at that thought), his wife Livia Giuggioli would greet the sight of him dishevelled every morning with an ironic, “Oh look, it’s Mr Darcy”. But, Firth says, “12 years on it feels like a school nickname you can’t shake. It occurred to me the other day to change my name to Mr Darcy and be done with it.” I laugh but he is serious, despite parlaying the Darcy image to his advantage in the Bridget Jones movies, playing Mark Darcy, much obsessed over by Helen Fielding’s lead character.

“The frustration is anything I do not on a horse looks a stretch,” says Firth, smiling yet serious. “When I did Fever Pitch, to get into my own jeans to play a guy living in North London where I lived, to play a character from my own background – people considered that a stretch.”

Well, it’s not that bad, I say. He’s about to play a Roman commander in The Last Legion and there’s a scene in And When Did You . . ? in which Blake masturbates in the bath. Firth shakes his head, smiles wearily. “Every single film since there’s been a scene where someone goes, ‘Well I think you’ve just killed Mr Darcy’. But he is a figure that won’t die. He is wandering somewhere. I can’t control him. I tried to play with it in Bridget Jones. I’ve never resented it – if it wasn’t for him I might be languishing, but part of me thinks I should do this postmodern thing, change my name by deed poll to Mr Darcy. Then people can come up to me and say, ‘But you are not Mr Darcy’ which would be different. I dare say it will be my saving grace when the only employment available to me is opening supermarkets dressed in breeches and a wig.”

Away from this half-jokey fretting, Firth is socially conscious. He has campaigned to stop the deportation of a group of asylum-seekers. He is the executive producer of a documentary at this year’s Times BFI London Film Festival, In Prison My Whole Life, about Mumia Abu-Jamal, a former Black Panther who has spent more than 20 years on death row for the murder of a policeman. (Giuggioli is producer.)

Firth is clearly an intense thinker and considers everything – family, career, politics – quite deeply. Morrison’s book made him pause before teasing his two younger children (he has three; a son, Will, by the actress Meg Tilly and two younger boys with Giuggioli). He jokingly agrees with “whoever said that when he upset his children he put a dollar in a jar for their future therapy”.

Firth’s own father is 73 and the Blake Morrison film “made me think we let our parents die with things unsaid”, but he cannot imagine a relationship with his father where “everything has been resolved”, even though they are close. Firth himself isn’t sure if he is a good father – “I’m not going to be writing the review on that one” – but says he tries to make himself “available” to his children. He reveals that he squeezed himself “into a bourgeois life to reach a sense of being settled”.

Why? “Serenity. When I was a teenager I romanticised the idea of artistically deranging oneself, whether it was a rock star f***ing himself up with drugs or Rimbaud’s conscious disordering of the senses. Being sane was a tedious, suburban thing to be. Unfortunately it’s not the brilliance, but rather the screwing up, that’s easy to achieve.”

He broods momentarily, agonises, looks down. “Acting messes with you. Whatever it is to seek that kind of attention is combined with the ability to play different characters – so there’s something fractured there. You take a person like that, subject them to all the vicissitudes of praise and attack and critique and you are going to wreak havoc with people who aren’t stable.”

Is he talking about himself? “Yeah . . . I didn’t go off the deep end. But it gets lonely. There came a time where I wanted to settle down. Excessive praise is like a drug but it doesn’t stay around for long. People can’t come with you while you’re up your own a***. If you want to have any companionship you have to have a little bit of generosity.” So he’s created “new disciplines” to maintain close relationships.

This is said in a halting mumble. It reminds me of the gruff intimacy between Morrison and his father in the film – that particularly masculine trait of revealing something heartfelt by sounding as determinedly unheartfelt as you possibly can.

And When Did You Last See Your Father? is released on Oct 5, 2007

Darcy does . . . Darcy

Another Country (1984) Darcy in training: Firth’s first experiment with a furrowed brow (committed Marxist-style) and pairs with it the gentlemanly, earnest, dignified gaze he would practice in . . .

Pride and Prejudice (1995) The lake scene has been replayed a thousand times on a thousand clip shows. Firth hones his stilted but honourable shtick.

Bridget Jones’s Diary/Edge of Reason (2000, 2003) Firth sensibly just gives in – the big D is given a modern update.

Girl with a Pearl Earring (2002) His Vermeer is the most charming painter ever on screen: terribly polite, slightly bumbling. Hmmm. Reminds us of someone. Love Actually (2003) Ahhh. Darcy’s language-barrier love.

And When Did You Last See Your Father?; The Last Legion (both 2007) No more Mr Wet Shirt Guy. Firth does serious and modern and Roman and butch.

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