Tartuffe, Lyttleton Theatre, London

From Men Behaving Badly to "Man of the Cloth Behaving Badly": that's the leap Martin Clunes is making now at the National Theatre in Lindsay Posner's hilariously trenchant and upbeat revival of Molière's great anti-fundamentalist comedy, which was premièred, nervously banned and eventually reinstated at the court of the absolute monarchs' absolute monarch, Louis XIV.

With his trademark jug ears hidden under a greasy flaxen flop, but with his equally idiosyncratic blubbery lips and infant-school painting of a face well to the fore, Clunes plays the spiritual adviser whom the ludicrously suggestible and direction-hungry Orgon installs in his house, much to the discomfiture of his family.

This is not the first time a figure from television comedy has been lured on to the boards to impersonate Molière's dodgily corrupt 17th-century cleric. A decade ago, Peter Hall persuaded John Sessions to take on the role in a low-key Glaswegian Jack-the-Lad interpretation. The translator on that occasion was Ranjit Bolt and it's a very sparky revised draft of that version that verbally animates this new Tartuffe.

The gingered-up adaptation wittily takes on board many things, including the disingenuousness of New Labour. In this comedy about extremism, there's now a pointedly tongue-in-cheek exchange at the end where people express the hope that Tartuffe will "return one day/ – Don't tell me to the Middle Way".

Clunes is terrifically funny in the title role. Posner's production homes in, more intelligently than any version I've seen before, on what is essentially comic in the potty dynamic between Tartuffe and Orgon (played as a twitchy, pop-eyed and cassocked Billy Connolly lookalike by the excellent David Threlfall). The show appreciates that Orgon is so prone to fanaticism that Tartuffe can lean back, as it were, against the boxing-ring ropes and relax as Orgon's absolutism fights itself to a crisp.

Oddly svelte and plummy-voiced, ridiculously Rasputin-like and built like a softly flabby sumo wrestler, Clunes performs miracles of laid-back, watchful acting. He is a revelation. In not trying too hard, he achieves wonders. Even when – stripped down to a wobbly loin cloth – he attempts to roger Orgon's wife (a beautifully spoken Clare Holman) with (unknown to him) her spouse secreted under the table, Clunes takes his time and is all the more amusing for it.

The set is covered with a jolting mix of 17th-century-style murals of episodes from the Passion of Christ and of neon-lit slogans and mantras of born-again Christianity – i.e. "Virtue Never Chooses Ease" etc. The most unsettlingly contemporary production of this play I have ever seen was Arianne Mnouchkine's in Paris in 1995, which translated the proceedings to North Africa, with Islamic fundamentalism the ideology that Orgon longed for and Tartuffe peddled. It would be a brave director who, against all the canons of political correctness, were to use that arresting trope now. Posner's production is the next best thing: heartily recommended.