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Role play: Laurence Fox on being Mr Billie Piper

He comes from acting royalty, was expelled from Harrow and loves an impromptu tattoo. Gerard Gilbert meets Laurence Fox, aka Mr Billie Piper

Sometimes I think they should teach psychoanalysis at journalism college; it would come in handy when interviewing someone like the actor Laurence Fox. Not that Fox is off his head – far from it – but there seems to me to be some interesting cross-currents swishing around his mental make-up.

In passing, he mentions that he is newly claustrophobic, taking the stairs instead of the lift all the way to the top of ITV's South Bank offices, one of the tallest office blocks in London, and he keeps referring to himself as OCD – that's to say, suffering from obsessive compulsive disorder – although he's using the term conversationally and not clinically.

He also chain-smokes Golden Virginia roll-ups ("It's not the nicotine; it's something to do with your hands", he says, "it's a nervous thing") and his body is liberally adorned with tattoos – the significance of which is sometimes lost on him the morning after the night before.

Fox at one point dismisses acting as "just a job", but then states that "I could give as good a Hamlet as any other fucker" (later on I get an inkling as to who these "fuckers" might be) before going on to call himself "self-deflating" and "my own worst enemy".

It's this complexity that seems to have fed into his playing of DS Hathaway, the theologically-trained junior partner in ITV1's successful rebooting of the Inspector Morse franchise, Lewis. Indeed Fox's Hathaway is a large part of the show's success – because after playing Watson to Morse's Sherlock Holmes for so long, viewers weren't going to buy it if Inspector Lewis (Kevin Whately) suddenly developed a mysterious past and a taste for Wagner.

There's a suggestion that Hathaway might be gay and this may have something to do with his crisis of faith, although Fox fights the writers to retain Hathaway's mystique. "The minute they put anything in I just say I'm not playing it," he says. "They do enjoy gently plugging away at my sexuality as much as they can, but Kev's got a very good philosophy on this – he says when shows start becoming about the main characters they vanish up their arses."

We have adjourned for lunch to a pub near ITV's offices, Fox making an increasingly rare visit to London to promote a one-off ITV Christmas drama, Fast Freddie, the Widow and Me, in which he plays a luxury car salesman who is convicted of drink-driving and sees out his community service order with a club for kids with learning difficulties. "He's a bit of a tool," explains Fox, as the pub starts to fill up with the studio audience from Loose Women. "I think the analogy for his personality is that he's one of these people who would speak to Stephen Hawking ve-ry slow-ly."

One of the children at the club turns out to be a bright teenager who has been in foster care all his life, and now has a terminal heart defect – "and my character does what any normal idiot would do," says Fox. "He buys a fake mum, and a fake family and fake home to spend his last Christmas." It's a redemptive Christmas tale, in other words, with antecedents in Dickens and Frank Capra, but kept from mawkishness by un-ingratiating performances by Fox and newcomer Jack McMullen as Freddie. And for Fox, it's a welcome break from playing Hathaway, who Fox calls "old dead eyes". I wondered if he was tiring of the role. "I would jump ship if there wasn't other work," he says, "otherwise you just vanish into one character and it becomes really dull because that character inevitably becomes you after a while – glib and annoying in my case."

This spurt of self-analysis brings me back to his earlier comment about acting being foremost "a job", an attitude I suspect stems from his background, of being brought up in an acting family – nay, dynasty. "Family of actors... a dynasty... I don't really know what it means," he says. "I suppose it's like coming from a family of undertakers."

His uncle is Edward Fox, star of The Day of the Jackal and father of Silent Witness leading lady Emilia Fox and up-and-coming talent Freddie Fox; his grandfather was the theatrical agent Robin Fox, while his grandmother was Angela Worthington, the actress of whom Noël Coward wrote the song, "Don't Put Your Daughter on the Stage Mrs Worthington". His father, James Fox, once the rising star of Sixties cinema, was so shocked to find his name billed above Mick Jagger in the extraordinary 1970 movie Performance – and perhaps by the diabolical undertones of the film – that he joined a religious cult and disappeared from view for a decade. "He's still deeply in it," says Laurence Fox of his father's Christianity. "Thank God as well, because he's a warm-hearted fucker, my dad, and they're not all – the Foxes can be a cold bunch of bastards."

Indeed there doesn't seem to be a great deal of brotherly love between James and Edward, whose relationship Laurence once described as "two big egos in a room". "When you hear them on the phone they laugh, but we don't gather as a family," says Fox now. "We don't see them over Christmas, for example, and I just always wonder if there is anything between them." "We", by the way, includes his brothers Tom (a landscape gardener), Robin (a film producer) and Jack (an actor – like his only sister Lydia). Fox is the middle child.

He was born in 1978, the year of his father's only movie during that decade – a film for the Billy Graham organisation – and grew up both teasing James about his faith and being teased about it. "We'd mock him," he says. "He's a good fun man to take the piss out of, especially his faith, because to properly take the piss out of someone you've got to go right to the core of him to the thing they hold most valuable.

"I think that people thought that Dad was a monk for a while, and, yes [there was] mild teasing – but I'm undamaged and it's nothing like you get these days. Much worse if you're one of these super-injunction parents and their kids are reading all about it on the internet. How hard that must be?"

His father's faith is now low-key ("You could probably go three or four months without the word 'God' coming from my dad's mouth; Mum would pray for a parking space"), but some of it must have got through because one of Fox's tattoos reads 'Psalm 139'. "It's an amazing piece of poetry, just stunning," he says. "I have tattoos everywhere now – whenever I get pissed near a tattoo parlour... they all mean so much when you get them done." Visibly inked on the inside of his lower arm is the inscription 'Mrs Fox 31.12.07', a tattoo made "over a boozy lunch in Mexico" to mark the date of his marriage to Billie Piper, the nation's Belle du Jour, Doctor Who sweetheart and the former Mrs Chris Evans. Piper apparently has a matching tattoo. "The cheapest tattoo in the whole world... not even straight, look how badly done that is."

The couple met in 2006 while co-starring in the West End revival of Christopher Hampton's Treats. "I literally knew within about five sentences," he says. "Just the way someone moves their hair, the way they speak, an inflection in their voice – it's not love at first sight, it's more if-I-can-do-this-I-can-do-it-with-you at first sight. I still feel exactly the same way today, which is lovely." And just in case that sounds too lovely, Fox adds: "She still irritates the fuck out of me sometimes." Like how? "Looking for her phone... stopping in the middle of the street when we're crossing the street and going 'Where's my phone?'. That sort of thing." And what irritates her about him? "I imagine I'm probably a difficult person to live with. I'm OCD – Winston's very OCD too, so she's got double trouble."

Winston is their three-year-old son (Piper, who is currently impressing theatre reviewers in the Almeida production of Neil LaBute's Reasons to Be Pretty, is four months pregnant with a second child) and the family all live in a country cottage in Midhurst, West Sussex, described by one visiting journalist as "more Withnail and I than Laura Ashley". "Yes, it is. If you have an open fire everything's dusty all the time so what's the point?"

He calls her "Bill" and she calls him "Lozza", and while "Bill" is away on the London stage, "Lozza" amuses himself. "I fish and ride and walk and drink a nice bottle of red wine and smoke fags by an open fire. I'm in bed by 10... it's pitch-black by five in winter and at half past seven you think, 'Wow, it's late'. I've learnt that when you're not working, trying to be active about it doesn't help and makes you very stressed and anxious and you start blaming your agent, so I just try to slow it right down and the country helps me do that."

And although Fox has finally watched his wife sporting an extensive lingerie collection in ITV2's hit drama Secret Diary of a Call Girl – something he resisted until recently – he still hasn't read Piper's very candid autobiography, Growing Pains. "I'm not instantly fascinated to be honest," he says, perhaps a little surprisingly. After all, who wouldn't be fascinated to read their wife's autobiography? "Another 25 years of never leaving the screen and I'll probably be in the autobiography club myself, but then I wouldn't remember anything anyway."

Any biography of Laurence Fox would probably have to start with his unhappy time at Harrow, the public school where he was sent by his father, who had an equally unhappy time there. Perhaps it was revenge for all that mockery. "I'll probably be sending Winston there," jokes Fox.

Raised to think for himself, he railed against the brutality of the fagging system, the unquestioning obedience and the snobbery. After an incident at a school dance (he claims to have forgotten the details) he was finally expelled, although allowed to take his A-levels as long as – rather sweetly – he spoke to nobody.

His grades were good (Fox says he appreciates, at least, the education he received) but the school's report meant he didn't get a place at university, spending the next two years living at home in Wimbledon, working as a gardener and then in an office analysing seismological data, of all things, and taking very long lunch breaks. "I'd light a massive spliff as I went to the pub, drink two pints of Stella really quickly, read The Sun, go upstairs to the abandoned fourth floor and have a doze until the end of the day. It was heaven."

Not so heavenly that he didn't realise that acting might have better prospects, although his first tilt at Rada ended in rejection, and his second attempt – successful this time – led to a not entirely happy stint at the drama school. If at Harrow he had suffered from snobs, at Rada he discovered the inverted variety. "It was never from people who'd worked hard and had come from little drama groups in Salford," he says. "It would be girls from Putney and stuff like that. I didn't have any middle-class friends at drama school.

"And all the way through I got deliberately niggled – and I think rightly – about whether I gave a shit or not. I remember having a lady teacher who said 'You shouldn't act... you definitely shouldn't act... I've watched you all this year and you've no access to your emotional life...'."

By his final year he was annoying his teachers by accepting work – his first role, molesting a 15-year-old Keira Knightley in The Hole and getting narked when the film's director announced that Knightley was a star in the making "and I'm going 'Why aren't you telling me I'm going to be a star?'." A part in Robert Altman's Gosford Park followed, and then a whole succession of British and German soldiers, including one in ITV's Colditz, which got him noticed by Kevin Whately and cast in Lewis. Just in the nick of time because, as Fox puts it, he had been hitting his "self-destruct button" and getting a bit of a reputation for it. Where does the urge to self-destruct come from? "I think probably Harrow would do that to you," he says.

Were his teachers at Rada right, I wonder? Does he maybe lack the ambition to go (as he once described Cate Blanchett) "gunning for an Oscar"? I quote back at him something he'd said about preferring to have a good time than be Daniel Day-Lewis. "I could do Daniel Day-Lewis's job as well as him," he replies. "Also I believe that Daniel Day-Lewis is a canny man. There are two main jobs in acting – the first one is to be a good actor and the second one is to convince everyone that you're a good actor. I'm certainly not going to sit around and weep for missing out on Troilus and Cressida at half past seven on a Sunday evening – I'd rather be sitting there working out what the best way of catching a pike in a snaggy weir pool is. I think it's more healthy for me."

Wife Billie Piper isn't, it seems, entirely sympathetic to Fox's self-estimation, and he tells me a story that ended with him describing a picture he'd seen as "ghastly". "Bill went, 'You think it's ghastly because you think you're better than everybody else'. And then I told this to my dad and my dad laughed so hard. My mum says it as well: 'You fucking Foxes... you all think you're so wonderful'; the irony is that we don't."

He is resolute that he's not a star ("it's only Lewis"), but two things happen at the end of our lunch that suggest otherwise. First he tells me of being in Ibiza the previous weekend and watching the Vaccines in concert. "We went to the after-party and the lead singer came running over to me and said, 'I fucking love Hathaway'. And I was like, 'I think "Post Break-up Sex" is the best song I've ever heard'."

The oldies love him too. As he's leaving the pub to have his photograph taken ("Be gentle with me," he says of our interview), the coach party from Derbyshire who'd been in the studio audience for Loose Women rise to cheer and say how much they love Lewis ("Better than Morse," says one, and I kind of agree). Left behind, I find his pouch of Golden Virginia on the floor – and one of the ladies whisks it away as a souvenir. Laurence Fox is a legend in his own lunchtime, at the very, very least.

'Fast Freddie, the Widow and Me' will be broadcast on ITV1 on 27 December