Comedy: We all like you, Jo. So why don't you?

In the 16th century, the prophet Nostradamus wrote: "The present time, together with the past, shall be judged by a great jovialist."

Many of the Gallic seer's predictions are subject to divergent interpretation, but there is general agreement among scholars that Jo Brand is the "great jovialist" of whom he spoke. Unfortunately, history can now confirm that the venue for this mighty judgement was not to be the Guildford Civic Hall.

For in darkest Surrey on Wednesday night Jo did speak of many things, but too few of them related to the weighty issues of the moment and too many to the very unmomentous issue of her weight. Now just as you would not expect to see Jack Straw out and about without his phalanx of trained attack-dogs, the prospect of a Jo Brand set without a single fat gag is probably too much to hope for. But on tonight's evidence, it is a possibility to which Brand should turn her mind with some seriousness. For if things drift much further in their present direction, people will start to worry that she has nothing else to talk about.

The Jo Brand of 1997 vintage is a far cry from the timid, self-abnegatory presence that can occasionally be glimpsed on old re-runs of Friday Night Live. She is currently one of the nation's best liked and most ruthlessly efficient comedians - these tickets do not come cheap and people are here because they are fond of her. So there is really no need for her to spend so much time anticipating negative reactions to her appearance by being more vicious about it than her most hate-filled adversary might be. The subversive effect of Brand's perpetual self-deprecation is not just subject to the law of diminishing returns - it might even be becoming counter-productive.

A strange and unsettling thing happens about a third of the way through the show. One of the small gang of vociferously drunk women without whom no sit-down, stockbroker- belt comedy night out is complete suddenly subjects the star of the evening to a volley of personal abuse, almost as if prompted to do so by the endless, genial, pre-emptive harping from the stage. The venue is so large that no one seems to hear, but the unpleasantness is genuine, and you can't help feeling that since Jo Brand is in a position to do whatever she wants, she needs to move on now before institutional status catches up with her.

It may well be that Jo Brand's public like what they know, but someone with her ability to overwhelm an audience - and of her contemporaries, probably only anal-sex demagogue Frank Skinner can match her in this regard - should be able to take them somewhere new every once in a while. Tonight she offers a few glimpses of what she can do, which is to say the unsayable in a way that makes it seem commonplace. (At one point Brand describes herself as being "at that age where if I don't have a baby soon I'm going to have to get one from outside the supermarket".) But this only brings into sharper relief the disappointing familiarity of so much of the rest of her material.

At her most mischievous, Brand still has an uncanny knack for mixing up those pleasures which are licensed with those which are forbidden - her description of the notorious sexual practice that is "the biscuit game" (in which groups of men masturbate competitively on to a wheat cracker), culminates in a triumphant "I managed to sneak in and grab the biscuit". But on the second night of a supposedly all-new nationwide tour, punchlines should not be hanging in the air before jokes are even set up. And this show offers no ready answer to the question playing on everybody's mind, which is: if Margaret Thatcher was the mother-in-law of alternative comedy, who will be the road-crossing chicken of the Blairite era?

Oxford Apollo (01865 244544), tonight; Watford Colosseum (01923 445000), Wed; then touring until 13 June.