Less Than Kind, Jermyn Street Theatre, London

The celebrations of the Terence Rattigan centenary won't throw up anything more enjoyably peculiar and intriguing than this novelty with which they now kick off. Less Than Kind is the hitherto unperformed original version of Rattigan's 1944 hit play Love in Idleness. A contemporary reworking of the basic situation in Hamlet, it centres on Michael Brown, an idealistic 17-year-old who returns from wartime evacuation in Canada only to find that his widowed mother is living in sin with the Claudius-figure, Sir John Fletcher, multi-millionaire right-wing industrialist and the embodiment of everything Michael passionately loathes.

Rattigan's biographer, Michael Darlow, has explained how the piece was hijacked by Alfred Lunt and Lynn Fontanne when they signed up to star in the West End premiere. To satisfy their demands, the dramatist sold out to commerce, transforming the industrialist into a good-hearted, worldly chap doing his best for England. The politics became less obtrusive; the values were turned upside down.

Working from the sole surviving copy, Rattigan's sometime lover and friend, Adrian Brown, gives the ur-draft its first airing in a production that is beautifully acted, full of evocative period detail and very funny, though you sometimes feels that you are laughing at the play as well as with it. Rattigan is said to have been broadly sympathetic to the ideas Michael espouses, such as the need for central planning in the post-war reconstruction. Odd then that he portrays his youthful idealist as a monstrous, haranguing little prig who spouts dialogue that sounds like a collaboration between Frank (Billy Bunter) Richards and Friedrich (Communist Manifesto) Engels: "Oh, whizzo! There's an article by Professor Laski on the equalisation of exchange rates," he exclaims, brandishing the latest issue of The Labour Monthly.

Even when he's adopting a self-consciously Hamlet-esque "antic disposition", our hero comes across as fundamentally humourless. There's a faintly android quality to the performance given by boyish, pint-sized David Osmond. True, the play pokes attractive fun at the youth's self-righteousness. The trouble, though, is that you can't take him seriously for a second in his slanging matches with Michael Simkins's much more human and sardonically perceptive Sir John.

Sara Crowe is a delectably amusing mix of gently distracted scattiness and wry wistfulness as Olivia, the mother castigated for becoming "the parasite of a rich voluptuary". But as Olivia is fully prepared to admit that her love for Sir John is inextricably bound up with the chance it gives her of playing the society hostess, there is nowhere for the "closet" scene showdown to go. Nor did I believe that she would renounce lover for son and retreat from Belgravia to dingy digs in Barons Court where she seems to doing her bit for the brave new world by rendering dried egg omelettes even less edible and failing to learn to type. The old Royal machine used in the production is the one on which Rattigan's secretary typed up this play. Not quite the coup of featuring, say, the quill that wrote Hamlet in a revival of Hamlet. But then Less Than Kind is not Prince Hamlet, though it was meant to be.

To 12 February (020 7287 2875)