Thanks to Lorna for pointing out this interview with Matthew in today's Guardian.

Credit was already crunching when the cast pulled on their smocks and waistcoats to film Charles Dickens' Little Dorrit but the BBC's drama department cannot possibly have imagined how perfectly this tale of fraudulent financiers and tragic bankrupts would chime with the new hard times. And just as Dickens' honest but burdened hero, Arthur Clennam, is naively oblivious to the economic shenanigans unfolding around him, so too is the man who plays him.

Wanting more space for their young family, Matthew Macfadyen and his actress wife, Keeley Hawes, have bought a bigger house in south-west London, which is "really clever financially" he observes dryly, just when the economy appears "on the brink of the global collapse".

"We thought perhaps our industry won't ... " He tails off with a hopeful chortle. "Everyone likes to be told stories as they are being repossessed."
Little Dorrit, adapted by Andrew Davies, delivers its blend of timely relevance and Victorian escapism over 15 episodes on BBC1 this autumn. Macfadyen is delighted the drama has been given so much screen time. "They are wonderful gobbets of soap, really. And it comes on after EastEnders, so you get your fix," he says.

Macfadyen's Arthur, a lonely man in early middle age, returns to Britain after a long exile working in China, troubled by his father's dying words. He senses that his family has committed a great wrong that he must put right. Little Dorrit, a young woman born in a debtors' prison, played by newcomer Claire Foy, works for Arthur's terrifying mother. "Arthur would never imagine that Little Dorrit would fall for him," he says. "She falls in love with him and he doesn't see it, and that's the love story that goes through the whole piece. It's a wonderful Dickens potboiler, apart from anything else."

Macfadyen first came to the fore as the taciturn spy Tom Quinn in the highly successful TV series Spooks and made a notable, and equally taciturn, Fitzwilliam Darcy, wooing Keira Knightley in the film of Pride And Prejudice. He is 34, but has noticed the steadily rising age of the parts he is offered: "John, 40s, grey hair," he grins. "Slightly jowly, tired looking."

Even as a younger man, his good looks were leavened by something more interesting: an attractive melancholy. Which is perhaps why, in the coming months, he is playing - as well as Arthur - three very different characters, all men bearing burdens rather bigger than a large mortgage. A friend of mine reckons that this solemnity makes Macfadyen look a bit like a Moomin (those Swedish cartoon figures that look like hippopotamuses).

Macfadyen has a reputation for being "notoriously awkward", as he puts it - this is on the basis of an interview he did shortly before filming Pride And Prejudice, in which he confessed he had not read Jane Austen and defensively dismissed questions about how he would step out of Colin Firth's dripping shadow. So I am surprised when he enthuses about being likened to Tove Jansson's slightly mournful white creatures. "I like Moomins. I've got these fantastic Moomin mugs and bowls. My little boy examines which bowl I've given him to eat his Weetabix out of," he says. "So that pleases me. Matthew MacMoomin. That's nice."

Macfadyen actually turns white in Frost/Nixon, the forthcoming film of David Frost's epic TV interrogation of Richard Nixon; he bleached his hair and dons preposterously large spectacles to play a young-but-grey John Birt. It is a comical look - Macfadyen's entrance as the future BBC director general sent enjoyable sniggers around the preview screening I attended - but while Michael Sheen and Frank Langella will probably attract most critical attention for their impersonations of Frost and Nixon, Macfadyen's Birt, then Frost's producer and right-hand man, is subtle, serious and accomplished.

Frost/Nixon is adapted from the successful play by Peter Morgan about the 1977 television interview, when Frost was trying to reboot his flagging career and the disgraced former president hoped to redeem his reputation. Macfadyen watched it on Broadway, where he found the dramatisation of Birt "a bit risible" - reducing a serious investigative journalist to a "goofy Brit producer".

"I don't think Birt was particularly taken with that and nor would you be," he says. So before filming began, he met Lord Birt for lunch at the House of Lords. Rather than the actor scrutinising his subject's mannerisms - "I thought it shouldn't be just an impression," says Macfadyen - he ended up being scrutinised himself when Birt visited LA to see the final day's filming. "He was watching me do him, on a monitor. He was there with a burger. It was very nerve-racking actually." He felt "terribly" self-conscious; luckily, Birt did not witness the scene where Macfadyen's Birt rushes naked into the ocean to celebrate Frost's interview. Macfadyen blushes. "Oh Christ, I'd completely forgotten about that. The bum shot." Did Birt really do something so seemingly out of character? "He said to me, 'Well, it's the sort of thing I would've done, I could've done it,' so that was good enough for me."

Since he's come fresh from a film about the tussle between interviewer and subject, I wonder if Mcfadyen has picked up tips from Tricky Dicky on how to handle tricky questions. In Frost/Nixon, the ex-president throws his inquisitor off balance with abrupt questions about his private life ... "Done any fornicating lately?" says Macfadyen with a smile, giving an excellent impression of Langella doing Nixon.

Macfadyen himself is more subtle. He has the diffident habit of leaving uncompleted sentences hanging in the air, but he is a charming interviewee, modest, without taking things too seriously. Which might make you hesitate to intrude.

On the other hand, some stories are too romantic and intriguing to resist. Nearly seven years ago, so the legend goes, Macfadyen stood on the set of Spooks in the rain and declared his love for co-star Keeley Hawes. Hawes had very recently married her long-term boyfriend, Spencer McCallum, with whom she had a young son.

She responded in kind and Macfadyen and Hawes are now married and live with their two young children, Maggie and Ralph, and Mylo, Hawes' son with McCallum. Hawes' ex-husband lives nearby.

Tabloid fascination with this calm domesticity reignited earlier this year when it was reported that they all went out as a family and Macfadyen and McCallum even sloped off to the pub together. He looks a little weary when asked about this turn of events. "There isn't any story. We all get on. It's really aggravating all that. It's really shithead journalism. It's not an unusual thing - families that make it all right for the sake of the kids. The story is that there is no animosity. I never said that we went down the pub."

He sighs, and points out that none of the family courts attention and he and Hawes don't invite the celebrity magazines into their home. Does the continuing interest rile him? "It's not annoying, it's fine," he says. "It's irrelevant."

Two other new film roles see Macfadyen playing policemen. These, too, are roles where emotions are subsumed to duty and responsibility. In Incendiary, Macfadyen plays an antiterrorist police officer and Ewan McGregor's rival in love. McGregor embarks on a torrid affair with a young mother moments before her husband and young son are killed in a terrorist bomb at a football match. Macfadyen is cautious because he hasn't seen the final cut after a long editing process but says it was a "brilliant script" based on a wonderful novel by Chris Cleave, which had the misfortune to be published on July 7 2005, the day of the terrorist attacks on London.

His other celluloid copper is a police inspector in a new Miss Marple film. "Marple is like doing posh rep. It's such fun. It's so silly." He acted alongside Rupert Graves and kept collapsing into giggles. "We couldn't get through scenes without corpsing. I can't look at him. We can't really act together. We shouldn't any more because it's very, very difficult."

Macfadyen does not find it so difficult to act alongside his wife. He turned up in an episode of the hugely popular Ashes To Ashes, where Hawes plays DCI Alex Drake. "It's really hard when your other half is in it but I thought Ashes To Ashes was so clever and witty and creepy and funny and camp and silly," he enthuses.

He also played Hawes' screen husband in Frank Oz's Death At A Funeral, which was released last year. Macfadyen is one of the few likable things in the black comedy and I confess that I didn't enjoy it at all. "No. Yes. Lots of people have really ... " murmurs Macfadyen. "People were divided over it. It was a sublimely happy shoot. Hilarious script," he shrugs. "One of those things." Later, almost as an aside, he adds: "I'm equivocal about my performance in a lot of things."

There is no competitiveness in his household, not when he's playing Prince Hal in Henry IV at the National and not when he and Hawes are developing a burgeoning sideline in voiceover work. He recently provided the grave narration of The Blair Years documentary. "It's all acting. It's all cobblers," he laughs. He attributes his rich and rolling timbre - redolent of Alan Rickman - to smoking. "It does help. You think of all those rich, fabulous, fruity voices - the Gambons and McKellens - and they are all from years of..." He tails off again. "I gave up about four years ago. I still miss it." Meanwhile, Hawes does really well on the voiceover work, too: "She's been doing Lara Croft for the computer game. There's some peculiar fan mail coming through the door."

How does Macfadyen feel about his fans who have edited highlights of his brooding Mr Darcy into tribute videos backed by power ballads on YouTube? "I feel very flattered. I don't know, really." Do you get people wanting to mother you? Because you have quite a sad face, I say. He giggles. "Vulnerable, yeah. It's just weird. It's really peculiar. Because the lovely thing about being an actor is being anonymous, it's never having to explain yourself. And that's what I find interesting about actors or painters I admire. I don't want to know about their lives. I don't really want to know what Anthony Hopkins has for breakfast. It's kind of bollocks, isn't it?"

Soon, no doubt, Macfadyen will pop up in YouTube clips as a naked John Birt, frolicking in the ocean. Is that as far as his career nudity will go? "Who knows? The websites will have a field day, won't they?" He hopes the scene will be set to a very stirring, cheesy - and not at all melancholy - rock power ballad. "Europe! The Final Countdown!" he laughs.