One man stands out a little among the trim collars and sharply- pressed lapels of the crowd at Jack Dee's West End first night. He's a good bit older than the rest, with maybe four or five days' stubble, and an unsteady gait which confirms him to be approaching the final straight of the mother of all benders. Mumbling loudly to himself and checking what appears to be a prescription, he takes his seat near the front. A sad picture of lost self-control and solitary abandon, he is the opposite of everything this evening is supposed to about - the anti-Dee if you like - and everyone sitting within his restless orbit knows there is going to be trouble.

The Gielgud Theatre lights go down - an eventuality which the anti-Dee greets in a voice resonantly reminiscent of Paul Whitehouse's whiskey- addled Rowley Birkin QC in The Fast Show, but twice as loud: "Ah! The lights are down: the night's entertainment is about to commence!" Dee materialises, observing - with characteristically acerbic accuracy - that the pounds 400 suit he has bought in honour of his West End run gives him the look of a "Sainsbury's manager". The anti-Dee proceeds to echo his every utterance with a series of stentorian grunts: "What is this mere mumbo-jumbo?" "Does he call this sophisticated entertainment?"

There is nothing more damaging to the comedian's mystique than a section of the audience knowing something they don't, especially when that something is that this heckler is not of the common or garden, roll-over-and-die-on-first-contact-with- a-mild-rebuke-from-the-stage variety, but a card-carrying crazy man with a weekly travelcard to oblivion. For the old Jack Dee - buttoned up, everything honed and complete - this situation would have been grave indeed. His glacial facade of painstaking orderliness might easily have crumbled to scree in the face of such authentic disorder.

Over the past couple of years however, something has happened to Dee. It's hard to know what might have caused the transformation - finally acclimatising to fatherhood, watching himself look a little too dour for comfort on his Saturday night ITV variety show, even making tabloid headlines by rucking in a Soho street with the TV critic of the London Evening Standard - but the new-model Jack is much less uptight than the poker-faced churl of Widget renown. Engagingly rumpled and a good deal freer in the action than of old, the new mellow Dee has even taken to ending sentences "... and shit".

As if responding to this new and unexpectedly laid-back vibration, his would-be nemesis in the stalls falls into a deep and merciful sleep, leaving the comedian to go through his paces undisturbed. And very dandy paces they are too. Dee has strip- mined his marriage for a wicker-basketful of high-grade new domestic material, and when he's not exploiting his newly broadened range of voices and physical gestures to potent effect, there's always the trademark curled lip to fall back on. Dee's talent to abuse is seen at its most eloquent in his challenge to the magician David Copperfield : "If you can fly, do it outside - c'mon everybody, in the car-park ... Dave's gonna fly".

Having started out as arguably the first post-Alternative comedian, Dee has remained true to his apolitical roots, but it will be interesting to see how his stance adapts to the new political landscape. The Britain of bad service and underwhelming ambition at which he likes to look askance is based on a largely pre-Thatcherite model, but his decision to invite the audience to write him messages on a jotter-pad in the interval has a real hint of stake-holding democracy about it. And what is the people's message? "You look like Larry Hagman's lovechild".

Jack Dee: Gielgud, W1 (0171 494 5065), to 21 June.