Sam West: 'I'm cheap and available – tell your friends!'

He may be theatre royalty – and he observes the fashion for class – but the actor/director is more political than posh

On the most cursory of glances, it seems an unlikely fit. Actor-director Samuel West, owner of some of the nicest vowel sounds on our stage and Oxford-educated scion of famous acting parents, is off to Newcastle to direct Alan Plater's fierce modern classic about mining, Close the Coalhouse Door. Yet after just a few minutes' conversation, West, eloquent and personable, leaves one in no doubt as to his passionately held political and ideological convictions. He's clear what he would say to any who question his suitability for this job. "Their point would be? That I'm not authentic? I didn't believe in talking mice either, but I was still allowed to be in Narnia [as King Caspian in the television adaptation of The Voyage of the Dawn Treader]. You can't tell the story of mines without believing that most of the time progress was made at the expense of the people who were at the bottom and got paid the least. I believe that, so that means I'm allowed to direct the play!"

Belief in the project, for which Lee Hall has supplied additional material to Plater's blazing 1968 script, is something that West, 45, possesses in abundance. He's certainly done his homework, quoting frightening statistics about safety standards in Chilean mines, and providing staunch defence of the union movement, whose struggles and occasional triumphs down the decades provide the beating heart of the play. "If you want to use Conservative rhetoric, unions are the Big Society in action, people getting together to help each other for not very much money," he says pointedly. As a council member for the actors' union, Equity, and vice-chair of the National Campaign for the Arts, it's a point that matters dearly to him.

Lee Hall has provided staunch advocacy of mining before, in Billy Elliot and The Pitmen Painters, and I wonder aloud whether mining has, for us now, somehow come to symbolise something greater than itself, namely the death of a manufacturing and unionised Britain. "I think it does stand for something we fear we might have lost," West agrees sadly. "Part-time jobs, itinerant workplaces or service jobs don't breed unionisation – or community, or community spirit – in the same way."

All of which seems a good juncture to ask him for his views on the "actors and class" debate that has been rumbling in the media for some weeks, ignited by Downton Abbey's Rob James-Collier saying that it's harder for working-class actors and Dominic West (no relation to Sam) adding fuel to the flames by claiming "Old Etonian" is a label that provokes hatred. Sam West starts off by sidestepping the question. "Speaking personally, as somebody who does a reasonably good RP, I wish I was 10 years younger. When I came out of university, from about 1989 to 2002 nobody made anything but East End gangster movies. And now everybody's doing posh stuff and I haven't got any cheekbones any more! I've got my career in completely the wrong order!"

I suspect this won't be West's last word on the subject, and it isn't. "Shameless is the new Boys from the Blackstuff: there's certainly a change in the way the working classes are being portrayed on television. In our last government we had a home secretary who used to be a postman and now we've got the 19th Eton-educated prime minister, so Dominic might reflect on that. I hasten to add that I'm an enormous fan of Dominic's and I get quite a lot of his fan mail, so I don't want to diss him in any way!"

West returns from time to time to the subject of social mobility. "I think it's really important that what it's like to live in this country doesn't just become an upper-class narrative," he says at one point, before concluding as we part, "I really do think the things that make our society what it is are under threat. It should be about everyone having the potential to be what they're going to be."

What, then, does he think about our current televisual fixation with the rigid class hierarchies of the past, in Downton and Upstairs Downstairs? He confesses that he doesn't watch the programmes but hopes they're not a reflection of an idea that this is the way things are supposed to be.

"I wonder whether we look back to a time of supposed certainty, where people knew their place, because we don't know our place at the moment and looking into the future is difficult. The really interesting thing about reviving a play written in 1968 is there's a much stronger feeling of potential and hope for the future. At the moment we are having to face the known possibility that we are passing on to our children a less good world than we inherited. I don't mind people being at the top of the ladder, I mind them pulling it up after them." Would he ever consider a role in period dramas like these? "Of course. I'm cheap and available – tell your friends!'

Despite fluctuating demand for cheekbones and RP, West has enjoyed a wonderfully varied career as an actor, director and voiceover artist. One of his earliest roles, as Leonard Bast in Merchant Ivory's exquisite film adaptation of E M Forster's Howards End, led to a Bafta nomination and with it the chance to try to crack Hollywood. However, after discussing the possibility with his parents, Prunella Scales and Timothy West, he chose to stay at home.

Does he regret that? "Only in so far as one regrets the things one hasn't done just because one hasn't done them. When people say, 'If I had my life over again I wouldn't do anything different', well, I'd do everything differently just for the variety'." This course of action, he says, meant he didn't have to "risk failure" in Los Angeles. Is he scared of failure? "Not as much as I'm scared of success," he replies emphatically.

Success happened over here anyway, with acclaimed turns as Richard II and Hamlet for the RSC and, latterly, with the "performance of his career", as one critic described it, as Jeffrey Skilling in the multi-award-winning Enron. He also had two years as artistic director at Sheffield, before disagreements with the board ended his tenure. Did he enjoy being at the helm? "Modified rapture," he says wryly. "It was awfully difficult and I messed up a lot of things about it." Nevertheless, he'd like to run another building some day and I suggest that the Almeida, just over the road from his Islington flat, might be the perfect fit.

West is disarmingly honest about the benefits of having parents well established in the family business. "It certainly got me auditions, but I don't think it ever got me jobs. People wanted to meet me because they knew my parents, yes." He claims that all his professional ambitions – "to be in Doctor Who, play Hamlet and read the shipping forecast" – have been fulfilled. So what about doing a Glenda Jackson and going into politics? "Being a frustrated idealist backbencher, like many of my favourite MPs, would sometimes be hell on earth," he says ruefully. Anyway, for now, Sam West is gloriously content with taking a play about coal-mining to Newcastle.

Close the Coalhouse Door is at Northern Stage, Newcastle, 13 April to 5 May (0191 230 5151, northern stage.co.uk), then tours nationwide until 30 June