Current reigning Oscar champion Colin Firth walked into a suite at the Soho Hotel yesterday to find a bunch of journalists chatting about Wimpy. There's a shot of the maligned British burger joint in Firth's latest movie - ensemble spy thriller Tinker Tailor Solider Spy, directed by feted Swede Tomas "Let the Right One In" Alfredson - and the mere mention of it was enough to set us all off on a nostalgia trip, to which the actor duly contributed. "I was just talking about Sherbet Fountains and the surprising things that don't change. You don't need to be nostalgic about Sherbet Fountain because it's exactly as it was." But after these comforting words of reassurance, a sudden sense of loss grips the actor: "There are still Curly Wurlys aren't there... or have they gone?" he asks. We assure him that they are still very much around, allowing the interview to proceed along a much steadier - if less frivolous - course. Despite the heartening presence of Wimpy, the 1970s set Tinker Tailor Soldier Spy offers little reason to be nostalgic. Firth may be one of a dozen British establishment stars in the film (from Gary Oldman to Tom Hardy), but this isn't a glossy feel-good romp about the glorious past. In fact all the characters are ageing, lonesome, introverted and borderline depressive men who have been gradually worn down by years of betrayal, ideological disillusionment and the threat of death. Their workplace is - if you ignore the high-stakes nature of the job at hand - a banal, drab environment beset by petty office politics like any other, and their private lives are non-existent. "I do think it's a beautifully melancholic story and the thrust of it is emotional rather than intellectual," confirms the actor. "They're all profoundly lonely, I think that's what the film is very much about. To me it's a very moving and tender portrait of lonely men, disappointed idealists. I think Smiley is a study of loneliness in his idealism and romanticism towards his marriage and his view of marriage. He has a wife who betrays him and who he forgives all the time and I think he really does believe in the patriotic values of what he does and to see treachery in that area is heartbreaking. I think these are all men who've made considerable sacrifices in their personal lives to do what they do and I think that puts more emphasis on the fraternity they have at work. With such high stakes the sense of camaraderie is heightened and it's also heightened that it's dependant on secrecy... and to realise that one of them is betraying everybody, and might have been betraying everybody for many years, is not just a threat - it's also heartbreaking." Firth has been a revelation in the last two years, earning plaudits with his Oscar-nominated turn in Tom Ford's A Single Man before finally snaring that golden statuette for The King's Speech in February, yet he takes a much smaller character role here as part of a talented ensemble. "The idea of doing it seemed cool to me. It wouldn't have done 10 years after a fantastic TV series : it would seem suicidal and too close to that time to seem retro and far enough on to feel out of date possibly. But now that we're thirty years on the from the series it seemed like a really interesting time to do it. And then I heard it was Tomas Alfredson, and names like John Hurt and Gary - it was absolutely irresistible." Several times during the interview he enthuses about the benefits of being in such an ensemble, even if it means taking a smaller role than he is currently used to receiving: "It lifts your own game. It's something I realised at drama school: right at the beginning they told us, from a practical point of view, good actors on stage with you don't make you look worse. It's not like having to do a recital and not being very good at piano after someone who is good. You on a stage with someone who's better than you will make you better. It's how it works. It doesn't show you up. It has an effect of not just making you raise your game but it magically makes you look better as well: there's more authenticity in the room." As well from the lure of the people involved, the actor was also intrigued by John le Carré's novel and the aforementioned series, which he remembers having become part of the Zeitgeist growing up. " hadn't read it - I have endlessly now. I had seen the series, but I'm not sure I ever watched it at the time and in sequence... There are certain things that go so thoroughly into popular thinking that you almost can't remember if you've seen them - people talk about Fellini-esque without ever having seen a Fellini film and everyone knows exactly what they mean. I think that's a sign that something's made an impact. I do remember scenes between Terence Rigby, Alec Guinness and Patrick Stewart without knowing if I ever sat down and watched it. I remember it being in the air. I remember my father talked about it. It was endlessly present." For his character, Bill Haydon (played by Ian Richardson in the BBC series), Firth has some obvious affection: "He enjoys life. He's vain. He cultivates certain eccentricities as part of his vanity - he's not just a spy, he's a bit of a bohemian: he's the artist, he's the one who has a slightly flamboyant twist to the way he dresses and rides his bicycle into the office. And he's sexually active, let's say, very active. He's somebody that makes use of irony, which is probably very useful if you're a spy." Whilst the Pride and Prejudice star admits sharing some of that vanity and ego with his character, the similarity ends there. Firth is adamant he wouldn't succeed in Haydon's stylish brogues, if asked to spy for queen and country: "I've seen John Hurt on the subject and I'd have to echo him: I'd be crap. It's all very well to draw parallels with actors in terms of the fact we might be capable of duplicity and inhabiting other roles and interpreting other people's motives, but that doesn't mean we'd be very good if somebody pointed a gun at us or if we had to go through any personal discomfort." Indeed personal discomfort is not something one readily associates with an Academy Award winning actor, though Firth hasn't had time to assess how it might have impacted his career just eight months on. "I've done one film since then. It's too soon to assess it. I'm sure it's changed things in some ways - for better or worse I don't know - but I think everything that happens changes something. I don't know yet what to say about it." "I think you can either see it as a pressure to live up to something and choose properly, which is bound to go wrong, or you can see it as taking the pressure off and saying "well, I've got that now and I'll do whatever the hell I please" and that's a far nicer way to see it. The one film I've done this year was a farce - a farcical comedy - and I took enormous pleasure in it and loved having it change the tone. There is absolutely no possible way you can do a farcical comedy in response to : it's not in the shadows of that, it's something else. For the most part things don't change very much. Previous Oscar winners that I spoke to said that to me: in the end carry on doing what you were doing before. You'll have some flops." But you can make more money, right? "Briefly you probably can, but it's far more likely when the economy is healthy. That's supposedly what you do, but then again there are some films which don't have a big budget, don't have a lot of money to pay the actors, and if you want to do those..." It would be easy in the current political climate to try and sell this film as being especially of the moment. Though it's a temptation the actor happily avoids, preferring to look at things with much more perspective: "I think the sense of disappointment and betrayal has been around for quite a long time and I think there is a view that people were more naive and accepting about their leaders, but there's always been disenchantment and suspicion. Otherwise there wouldn't have been dissenting political movements through the centuries: and there have. So I think it's ongoing and I think it always feels current and it always feels at its worst." Though he's not suggesting the Cold War set story is no longer relevant. To the contrary: "I think it feels very current. If you take the Soviets vs the West out of this, I think all the other elements are pretty pertinent really. In particular you've got hacking - whether it's Wikileaks or journalists - and we know that this industrial espionage goes on and on, and we're all as paranoid and freaked out as we ever were. If it's not "reds under the beds" then we're worried about who is a terrorist and is our intelligence any good? So I think those things are very much alive when it comes to issues of trust and paranoia and the general state of neurosis." With those grim and gripping themes the going concern of Tinker Tailor Soldier Spy, it may prove a surprising and unsettling cocktail for those after a dish of frothy 1970s nostalgia. But Alfredson's film is is no way nostalgic: it's not necessary to get nostalgic about things that haven't changed, after all. Now where can I get that Sherbet Fountain? Tinker Tailor Soldier Spy is released in the UK from Friday 16th September. It's very good, as you can read in glowing reviews from our Adam Whyte and Shaun Munro. You can also find our previous interview with director Tomas Alfredson and screenwriter Peter Straughan here.