Jonny Lee Miller is shy. At least I think he's shy.

He walks into the central London hotel room in which I've been told to wait, hesitantly, semi-apologetically, head bowed and hand outstretched: "I don't know what you want 50 minutes with me for."

This throws me. I suppose because famous actors tend to be show-offs and showmen, but also because this is Jonny Lee Miller, aka Sick Boy, the cult Trainspotting character whose snarling Warholian image hung above my boyfriend's bed at university. He is the man who turned a peroxide-mopped miscreant into an emblem of Cool Britannia and was once a member of the redoubtable "Primrose Hill set". Jude Law remains his best friend, and he also had a short-lived marriage to Angelina Jolie. I don't know what I'm expecting, but it's not this polite, self-effacing man.

"Actually, shy is probably right," says the London-born 44-year-old when I tell him this. "I'm a little bit more relaxed these days. But I guess I'm still not that comfortable sitting here talking about myself."

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Jonny Lee Miller believes his job as an actor is to "fool people".

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In which case, we can ease into it with talk of his T2 alter ego. In Danny Boyle's long-awaited sequel to Trainspotting, his character, Sick Boy, now prefers to be known as Simon, and is running a pub, alongside various scams. He has aspirations (to open a brothel) but, 20 years on, "his maturity level is sort of stuck".

Miller says: "People thought Sick Boy was so cool in the first film, and I really wanted to get away from that."

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In Elementary, Jonny Lee Miller plays a modern-day Sherlock opposite Lucy Liu's Dr Joan Watson.

Which he does. One of the most poignant scenes in T2 shows Simon touching up his roots with a toothbrush, "because we wanted it to be clear that he was trying hard – only it's not quite working any more". And although none of the film's four lead characters – Renton (Ewan McGregor), Begbie (Robert Carlyle) and Spud (Ewan Bremner) – are thriving, Miller agrees that Simon is the saddest of them all. "Really, the only winners in the film are women," he points out. "And that's intentional."

Asked about the themes of T2, Boyle said: "It's about how disappointing men are." Miller agrees. "I think so many men have this really sharp feeling of being a disappointment in their mid-forties," he says. "There's probably something chemical about it – the drop of testosterone, the fact that you don't feel the same way physically. It's a real thing. You do tend to feel like a disappointment."

I'm surprised by Miller's strength of feeling. After all, the grammar school-educated son of theatre actors Anna Lee and Alan Miller from Kingston-upon-Thames seems to have done pretty well for himself. Thanks to his hit TV series Elementary, now in its fifth season, he's got a huge fan base in New York, where he's been living for 10 years with his wife, American actress Michele Hicks, and six-year-old son Buster.

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Thanks to the success of Elementary, Jonny Lee Miller has a huge fan base in New York now.

When I ask whether he's ready to be plunged back into the post-Trainspotting celebrity he must have experienced 20 years ago, he looks at me blankly. "Well, I left London to be with Angie in LA [that year]," he says. "So that took me away from all the hoo-hah around Trainspotting. But, anyway, I won't go into that."

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1996's Trainspotting helped propel Jonny Lee Miller to global fame.

"That" is presumably the Miller-Jolie coupling, about which little is known, aside from the fact that they met on the set of the 1995 film Hackers, and that for their wedding the following March, Jolie wore a white shirt of Miller's with his name scrawled on it in blood – 18 months later, they were divorced.

Wasn't the hoo-hah surrounding their relationship just as big a deal? "Well, there wasn't one, because we were both completely unknown. Angie wasn't...it was pre all that."

So they were able to have a normal relationship without the pressures she's faced since? "Oh, yes," Miller replies.

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Jonny Lee Miller's Sick Boy and Ewan McGregor's Renton reunite in Trainspotting 2.

Does he keep in touch with her? "Yeah – we're still friends," he nods, and before I'm able to ask whether he's spoken to the actress since the breakdown of her third marriage, to Brad Pitt, he throws me a small smile that says: "That's all you're getting."

Miller may have chosen a quieter path to success than contemporaries like Law and McGregor, but the complex characters he has played in less commercial films (Patricia Rozema's Mansfield Park, Gavin Millar's Complicity and Pete Travis's Endgame) have all garnered critical acclaim. Then there's the successful US TV career he has been enjoying since 2006, first with the surreal legal drama Eli Stone, and now with Elementary, in which Miller plays a modern-day Sherlock opposite Lucy Liu's Dr Joan Watson.

"I think I'm doing all right," he assures me. "In terms of success, I've been around long enough to know that it's a long game - and I want to be doing this until I'm old. I also think that if you want to be left alone, you can engineer your life that way."

He does this very well – and it's true that I've never seen him papped tumbling out of nightspots or indeed "attending any awards ceremony I haven't been nominated for". Miller tells me that "if people know too much about you, I think you become a little less interesting as an actor – your job is to fool people."

Even his Twitter feed is pretty impersonal – certainly in comparison to his T2 co-star, Ewan McGregor, who is fiercely opinionated on everything, particularly the recent women's march.

When I ask what the feeling in post-election New York is like, Miller winces and says: "I'm not going to get political."

Does he believe actors should avoid being political? "No – I think if you're a citizen, you have every right to get political about that country's politics. And I don't think that actors should be slagged off for using their voice. Meryl Streep had a right to say what she did," he shrugs. "She's a US citizen, that's her opinion and if you agree with it, good."

T2 may not quite hold itself up on its own merits, but as a nostalgia-fest in which you are, as Simon tells Renton in the film, "a tourist in your own youth", it's a charm. The acting is superb and the cinematography slick, but some of the drug-taking montages have prompted the same questions that Trainspotting did about whether the films glamorise drugs.

"Danny [Boyle] is obsessed with the truth, and I do think the bottom line is that if you're trying to be truthful, then you're going to be OK. So if you're running around saying 'Isn't heroin cool?' and just showing people having a great time on drugs, then yes, I think it would be irresponsible – and also not truthful.

"But, as with the first film, we were confident in our attitude towards it, which wasn't reckless. You're trying to show the attraction people felt to drugs and the buzz they got from them, as well as the consequences – and the devastation."

A publicist pops her head around the door, signalling the end of our interview, and although I haven't learnt a great deal about Miller, I like what I do now know. Furthermore, I suspect we'll all enjoy being "fooled" by him for years to come.

Season 5 of Elementary begins screening on Prime at 9.35pm on Sunday, February 12. Trainspotting 2 (R16) opens in New Zealand cinemas on February 23.

 - The Telegraph, London