Julia Roberts, another illustrious co-star, has been keeping tabs on her Irish accent with the aid of tapes made by Spitting Image voiceover artiste Kate Robbins. Hart can't get rid of his. In conversation, his customary Liverpudlian makes random leaps across the Irish Sea. In the midst of his fifth back-to-back film role, a degree of confusion is understandable. Hart is just back from a tricky weekend of rapturous Venice Film Festival acclaim, promoting a Channel 4 production called Nothing Personal in which he plays a psychotic UVF man called Ginger. He is still fuming about being denied access to his hotel full of free-loading revellers after a hard day's European press.
"You have to keep reminding yourself that things aren't fair," he fulminates with a bitter twinkle. "Oh sorry, I forgot, here was me thinking that things were going to be in some way equitable." Level-headed to the point of pessimism about the sudden upturn in his fortunes - "Next year it'll be someone else" - this man is in no danger of losing his grip on reality. "After they've achieved a certain something," he observes, "people always say that they planned it in advance - they knew what they wanted each step of the way and then they went for it - but I'm sorry, what happened to me was a random series of events and a great deal of luck."
What happened to Hart was that a film he had almost forgotten making finally came out. It took five years for The Hours and the Times (Christopher Munch's arty, no-budget exploration of the relationship between Brian Epstein and the young John Lennon) to get a proper showing, but when it did, Hart's gawkily magnetic Lennon quickly won him a second shot at the caustic Beatle. In the brighter, brasher, bigger-budget Backbeat, he again brought something to the role that it wouldn't have had without him - cocksure and vulnerable is a tough turn to master. Hollywood, and type-casting, beckoned. For which loveable mop-top did the producers of Forrest Gump want Hart to supply the voiceover? It wasn't Paul McCartney.
After 10 years of on-off work in British TV, type-casting of a marginally less specific variety was nothing new to Hart. "All I did was car thieves," he observes darkly, "because that's the way the British TV audience seems to perceive people from Liverpool ... it's humiliating." Wounds still raw, he recounts a typical casting call, for the Manchester-based doctors and nurses show Medics. "I went in for the audition and the director, who was from London as they usually are, said 'You're from Liverpool, great, yeah, we could change the villain to being from Liverpool' - as soon as he heard my voice the whole thing made sense to him." It must be nice to provide such certainty. "Do you know what I mean? It's like, no, I'm an actor, a Manchester accent is a thing you do with your voice - it does not require surgery."
Having subsisted throughout the late Eighties and early Nineties on the dole, self-started local theatre projects and odd bits of television (the oddest being the last episode of Albion Market and a three-week cameo as a traveller in EastEnders), Hart's devotion to his craft cannot be questioned. Acting was not in his genes either. He grew up in the Ken Dodd-stigmatised Knotty Ash district of Liverpool. His dad worked at Fords, his mum did "bits and bobs at the blind school", and he went to an old- fashioned Catholic grammar school run by priests for whom, Hart recalls drily, "beating people up was a matter of course".
The school play in his last year there gave Hart his first part, in Gogol's Government Inspector. "I only went to the audition with the intention of ridiculing my fellow students," he remembers, almost shame-faced. "It was the classic 'You think you're so smart, why don't you come up here and have a go' scene. It's the oldest, saddest cliche in the book, but in my case it sadly happens to be true." He started going to the Everyman youth theatre, where he was pleased to encounter several local acquaintances who had somehow neglected to mention that they too had got the acting bug.
Films were already something of an obsession. He'd get the bus into town three times a week - often still in uniform - to the five o'clock show of "whatever they'd let me into". Fourteen years old and marvelling at Apocalypse Now on the screen of a huge, deserted Liverpool ABC, the notion of actually being up there oneself must have seemed at best unlikely. "Two films which really made a difference to me were Kes, which I saw on the TV, and especially Gregory's Girl, in that it was British people my age and younger on the screen and it wasn't the Children's Film Foundation [Hart switches into a deadly pastiche of the CFF]: 'Those guys over there look suspicious - it's a good job your dad's the chief of police!' "
When he is not being extremely serious, to ensure no one pigeon-holes him as a chirpy scouser, Hart can be very funny. He is also currently riding the crest of a healthy wave of new British cinematic endeavour. "Things are a great deal better now than they were, say, three years ago," he says happily. "It's like punk - there was such a stasis, such a bad vibe of just nothing going on, that something had to happen." And whatever does happen in British film terms at the moment, Hart seems to be somewhere near the middle of it; from a dextrously heart-string plucking cameo in the fine The Englishman Who Went Up a Hill and Came Down a Mountain to a bold if unequal struggle to lend resonance to the lead role in Vadim Jean's creaky Clockwork Mice.
Broader exposure beckons for Hart's compellingly edgy, vaguely stoatish screen presence in Loved Up - the BBC's imminent, tabloid frenzy-inducing "sex and Ecstasy" slice of life drama - and Angela Pope's The Hollow Reed, in which he co-stars as the gay lover of charismatic Hal Hartley regular Martin Donovan. But his biggest role yet is at the centre of Ken Loach's surprisingly gripping Spanish Civil War epic Land and Freedom, in which Hart excels as an idealistic Scouse communist who goes to fight in Spain and watches his illusions go up in Stalinist gunsmoke.
There is only one cloud on Hart's horizon at the moment. It's that moustache. It's horrible. Happily, it turns out to be born of professional necessity rather than personal choice. "Michael Collins is set in the 1920s when there were a lot of moustaches about, but none of the famous actors wanted to grow them, so everyone else had to." Would Hart be prepared to go to Hollywood for a chance to join the clean-shaven classes? "I'll work in America tomorrow if a good script comes up, but I don't want to go over there, get poor again and end up in an episode of a sitcom as a Beatle."
8 'Loved Up' is on BBC2, 23 September. 'Land and Freedom' opens 6 OctoberReuse content