A Voyage Round My Father, Donmar Warehouse, London <!-- none onestar twostar threestar fourstar fivestar -->

Life with the Mortimers

John Mortimer's blind barrister father bequeathed him an overdraft. But he more than made up for the pecuniary shortfall by also leaving him a house and flourishing garden (where the author still lives) and almost absurdly rich material for his writing.

It's not just that Mortimer Snr had the kind of in-built theatricality that practically transposes itself to the page and the stage. What makes him endlessly fascinating and infuriating and tragicomic as a character is the fact that he remains, fundamentally, an enigma.

His blindness was a subject that could never be mentioned at home. He would rage against petty things (cold plates, runny eggs) but never against the universe in which accidents such as the one that left him sightless occur. Why this aversion to mentioning anything unpleasant? Was it a case of "courage, cowardice, indifference or caring too completely", the grown-up son asks in A Voyage Round My Father, Mortimer's wonderfully funny and touching play, which Thea Sharrock now revives in an assured production at the Donmar Warehouse.

The underlying mystery is honoured in Derek Jacobi's fine portrayal. He's not as frightening a figure as Olivier was in his incomparable impersonation in the television version, and for my taste he's too actorly.

Yes, to be sure, the father had mastered the thespian skills needed to dominate a court, and there's a very amusing scene in which the son (sympathetically played by the excellent Dominic Rowan) tries, with a farcical lack of success, to copy his father's tactics (such as counting to 43 to unnerve the opposition before beginning a cross-examination) on a case of his own. But Jacobi occasionally gives the impression that the man had been to Rada.

Where he scores is in brilliantly suggesting the tension between outrageous selfishness and a kind of profligate largesse in the character's non-stop peppery performance. You feel that here is a person who has never bothered to grow up and expects to be treated as a law unto himself and yet has somehow managed to achieve a patchy wisdom precisely through bypassing conventional adulthood.

There's a devastating moment when the son's new wife (a nicely tart Natasha Little) refuses to play along with the family charade of ignoring the blindness. "Why do you bother with all this gardening when you can't see it?" she asks. Jacobi brings out the superb, disarming lack of self-pity, the moral authority and the cunning of the father's response as he commands her to take him to the West Copse and "be my eyes".

A Voyage Round My Father is a memory play in which narration from an adult son is combined with scenes involving his younger self. It has an almost revue-like structure and in this it compares unfavourably with Peter Nichols' Forget-Me-Not Lane, another comedy about a life dominated by an overbearing and impossible patriarch.

The latter brings past and present into much more dynamic collision, though, as memories of the author's wartime adolescence hurtle through a semi-circle of doors and start talking back to the hero. This dramatic conceit is an ideal way of illustrating how the past nags away in the mind with unfinished psychic business. It also highlights how we only properly understand our parents when it is too late to be of any use.

Mortimer's overly discursive piece is acute, though, about the ambiguous legacy left by the father. The new wife complains that the rituals of home - the constant game-playing, the jokes, and the implication that seriousness is a faux pas - are in danger of stunting her husband's writing. But Mortimer sticks up for these values, while going beyond them in this play.

His widowed mother refused to watch A Voyage Round My Father, thinking the very idea of it was as vulgar as having a swimming pool. Once fancies that the father, though, would think the piece a fitting monument, while refusing, of course, to admit it.

To 5 August (0870 060 6624)