What do you think of when you hear the phrase 'white working class'? Tattoos? Dangerous dogs? Shellsuits? Scratch cards? Chips? Binge drinking? The BNP? It would be no surprise if the images conjured are negative; in the past four decades, the image of the white working class has gone from hero to less than zero.

In these tolerant days, the one underprivileged group that it's OK to find intolerable is the white working class. In our multicultural society, they're the unlucky ones deemed to be without a culture. Last year, for example, the editor of Eastern Eye went on television to condemn Channel 4 for allowing 'illiterate chavs' on to Celebrity Big Brother. Eyelids remained unbatted. Trevor Phillips was not called upon to issue a statement. The Sky News presenter to whom this comment was made simply nodded his head in silent agreement.

But it wasn't always open season on proletarian whites. Back in the late Fifties and early Sixties, the working class was flavour of the decade. Films such as Saturday Night, Sunday Morning found something noble, if harsh, in the condition of the indigenous poor. The theatre was filled with angry young men with earthy accents railing against the class structure. Pop music was transformed by cocky lads from humble backgrounds, as were photography and advertising .

A working-class hero was something to be, as the only middle-class Beatle, John Lennon, later sardonically sang. And then, almost overnight, white and working class became a deeply unfashionable combination.

That list of cliches I suggested at the beginning nowadays regularly features in film and TV drama as shorthand for 'white trash'. And even in the case of original art, such as the photographer Richard Billingham's Ray's a Laugh series or Paul Abbott's Shameless (in both cases, significantly, the artists come from the background they document), the characters can't quite transcend the squalor of their setting. For all their spirit and spirits, there's something resigned, if not quite hopeless, about the Gallaghers in Shameless

There is also, of course, EastEnders, an ersatz version of a vanished east London, in which the cast are simple ciphers for politically correct issues, with some domestic histrionics thrown in for drama's sake. I could go on but, nah, leave it, it ain't werf it.

Back in the Sixties, there was a nobility to the working class and also, crucially, a mobility. It was on the way somewhere. But that optimism has gone. Those who could get out have left, joining an expanded middle class, and those left behind have become the underclass: ugly, obnoxious, feckless and amoral.

Not untypical in this regard is the stepfather in White Girl, a drama that forms part of next week's BBC2 season on the white working class. He's a drug-dealing, wife-battering, shaven-headed, racist psycho, with a hint of paedophilia for good measure. The only way out for his illiterate, alcoholic, racist wife and scowling stepdaughter is the benign sanctuary of that well-known religion of female liberation: Islam.

Every Muslim in the play, written by Abi Morgan, is polite, considerate and possessed of saintly forbearance. Quick thought experiment: can you imagine the reverse scenario being presented in a TV play? Zen chavs and vicious, uncouth Muslims?

The season, says the BBC, 'explores the complex mix of feelings that lead some white working-class people to say they feel under siege and as if their very sense of self is being brought into question.' Cue Union Jacks fluttering wistfully in bleak suburban winds.

But there's nothing complex about White Girl and it will do little to ease that sense of siege. So determined is it to bring the white working-class sense of self into question that its answer is a conservative and sexist religion. In this sense, the play exemplifies the changed attitude that the liberal arts community has shown towards disadvantaged whites since the Seventies. It was around then that ethnic groups began to gain priority in artistic sympathy and poor whites became the sinners more often than the sinned against.

Perhaps you could trace the decisive moment to Enoch Powell's infamous 1968 speech, which is revisited in the documentary Rivers of Blood. An intelligent attempt to unpick the truth from the legend, Denys Blakeway's film reminds us of the working-class backing for Powell, which saw dockers and meatpackers marching in his support.

On some atavistic level, immigration was perceived as a threat to identity. There are many reasons to dismiss this fear as ignorant nonsense, but in a cultural and, indeed, artistic sense, there seems little doubt that the white working class has subsequently suffered an identity crisis. You can see it in the content of this season - there's nothing celebratory here - and you can see it in the bemused, uncertain faces that populate Marc Isaacs's documentary All White in Barking and Henry Singer's Last Orders, a film about the decline of the Wibsey Working Men's Club near Bradford. An atmosphere of displacement, or impending obsolescence, hangs over these communities, as if they've lost their purpose.

There will be those who will put the whole malaise down to politics and economics - 'It's all Thatcher's fault!' - but close observation reveals something else in these films. In All White in Barking, a white woman working in a traditional butcher's going out of business is asked whether she'd eat pig's ears. It's obvious that she's repelled by the thought, but she also knows that it's wrong to express a critical opinion about another culture's tastes, so she timidly says that she doesn't eat much meat.

There's a lot of this kind of doubt and prevarication, which may be an improvement on crass racism but doesn't exactly signify self-confidence. The exception is an ageing character named Dave, gruff, opinionated and a supporter of the BNP. He's as unrepentant as he is unenlightened and yet there is an admirable, even charming, candour to his manner. At least he doesn't pretend to be what he isn't.

Dave has a half-black grandson from one of his daughters and his other daughter is going out with a boy with African blood. He obviously adores his children and grandchild, but he moves to Canvey Island to get away from non-whites and immigrants. There, he stands on the grim Essex beach vainly trying to hold back the tide of history.

Yet in Dave's story, we see, even if he can't, the hidden success of multicultural Britain. Not the tolerance and respect for separatism as preached by archbishops and playwrights, but the messy, difficult and tense business of living and loving together.

It's the children of people such as Dave who live cheek by jowl with new arrivals and adapt to rapid change. They are the ones who really embrace people from other countries and cultures by forming relationships and raising children together.

Meanwhile, the liberal arts community, for all its eloquence in anti-racism, is far more inclined to retreat to private schools and affluent enclaves, the better to maintain a homogenous culture while pronouncing on the benefits of diversity. It's fitting, therefore, that it's the BBC that's screening this season. For it was that progressive home of liberal arts that Greg Dyke, the former director general, so tellingly described as 'hideously white'.

· Andrew Anthony's The Fallout: How a Guilty Liberal Lost His Innocence, is published by Jonathan Cape