Richard Herring, Leicester Square Theatre

Is it legit to joke about races and creeds and the parents of infamously abducted children? What’s the difference between Carol Thatcher using the term “golliwog” and Richard Herring doing a routine about having his iPhone stolen by a kid on a bike who is, incontrovertibly, of Afro-Caribbean ethnicity? The answer is it’s all about intention. Which is where the moustache comes in.

In cultivating a small trim growth on his upper lip, Herring has alighted on a symbol that can go one of two ways. Depending on whose face it’s on, it represents either murderous evil or sublime comedy. But the global perception is that the dictator trumps the tramp. No one calls it a Chaplin moustache. Herring's avowed intention, in going about his daily life with a semaphore of racial hatred sprouting in the middle of his face, is to reclaim the toothbrush tash. “It’s a big commitment,” he concedes, “to make what is essentially quite a glib point.”

Herring is halfway to deNazifying this potent symbol there when he walks onstage. His publicity shot suggests he has gone to some effort to train his hair into a Hitleresque comb-across. Live, the rest of him looks a lot more like Chaplin’s shambling hobo – so long as you overlook the generous midriff. It turns out that there's rather less comedy in the public's muted reaction to that one unshaven square inch than in Herring's anxiety that a patch of his face hints at Holocaust denial. What will posterity say about him if he turns up with a Hitler moustache to his parents’ golden wedding? How can he not be taken for a racist, looking like that the day after the BNP have won two seats in the European Parliament?

Hitler Moustache trespasses deliberately close to the acceptable limits of comedy. Before he tells the McCann joke he asks the audience if they want to hear it. That the vote is overwhelmingly in favour neatly illustrates a point: this is comedy that holds up a mirror. He proceeds to invert the logic of racism. Wouldn’t you rather, he argues, hang out with someone who hates only half the human race than, say, all of it? And how about the man who sees all Asians as Chinese? That surely suggests a mentality which sees past difference rather than insists on it.

There are of course digressions along the way, including pleasing asides about other comedians – he particularly wonders just how much of the irony Al Murray’s vast fan-base understands. He gets wonderfully lost in a Socratic dialogue about political correctness with a fictional version of himself. Now and then the seriousness of his intent reduces the gag rate and, in a style of delivery that is already relentless anyway, Herring harangues. He even admits it. “There aren’t really any jokes in this bit,” he says, and cites as his defence the conclusion of The Great Dictator, in which Chaplin halted the satire to deliver an impassioned defence of liberal values.

Herring’s comparable mission becomes ever clearer. This is stand-up aimed squarely at Generation Y. Our forebears flocked to Spain to fight the right-wing threat in the 1930s. These days the politically apathetic cite their democratic right not to have to wander down to a local school and put an X in a box. All good news for the BNP. You wish Herring had been there on Question Time to give Nick Griffin a bloody nose. He beautifully deconstructs the BNP's appropriation of Spitfire as a logo, and their ludicrous claim that immigration first became a problem for these isles several thousand years ago.

Herring concludes by asking his audience to pick up a stick-on moustache from a bucket on the way out and reclaim it for comedy. Or attach to a poster of Jimmy Carr. A useful show.