Of Way Upstream, first seen in Scarborough in 1981, Alan Ayckbourn has said: "It was an attempt to get away from what I had been writing. It's an adventure story. I was beginning to be of the opinion that the theatre's salvation lies in a move away from the over-emphasis on the verbal, back towards the visual."

At the National, it was also famously almost a move into the soggily tactile, for this is the play which involves flooding the stage and putting a mobile cabin cruiser on it. Scarborough, being a coastal town, has some knowledge of the vagaries of water and coped perfectly - as it does again. The National sprang leaks and all but disappeared into the Thames.

Business partners Keith and Alistair, with their less-than-enthusiastic wives, set out for seven days' cruising up the River Orb (get it?) to Armageddon Bridge (get it?), leaving behind them their factory gripped by industrial strife. At stopping points along the way - this being 1981 and mobile phones not yet invented - they are caught up by Keith's secretary bearing the day's news of fresh disasters back at work. Keith, it should be stressed, is your strongman boss with no time for union interference, whilst Alistair is more appeasing. The wives broadly reflect their respective spouses' natures, Keith's June being brashly assertive and forever complaining, Alistair's Emma quietly accepting - but cautiously, constantly, wearing her life jacket.

So far so good. But suddenly, in the second act, we are thrust from relative realism into a J M Barrie world of allegory. The cruiser is hi-jacked by a couple of pirates - "river spirits of evil," as Ayckbourn has characterised them - who are supposedly a violently right-wing girl and a violently left-wing man (though he's more fascist than left-wing), and who create chaos and destruction. In the midst of this sit Alistair and Emma, meekly hoping it will all blow away and sweet reasonableness prevail. "The only people who get heard in this world are the extremists," says Alistair. "They're the only ones with the energy to shout loud enough." Until, that is, even he is pushed too far and goaded into insisting on a Third Way.

Perceived at the time to be Ayckbourn's agonised screech against Thatcherism, Way Upstream was labelled his 'SDP play' on its first outing. It emerges more strongly today as a study of leadership in its various forms. But for allegory to be successful, the surface myth needs to be credible in its own right as well as its symbolism: here, unfortunately, the myth is ultimately a bit silly.

Ayckbourn's production of his own play is fine and gives it every chance to succeed. The technology works faultlessly and is genuinely spectacular. And, if there is a tendency by some members of a generally excellent cast to overplay their lines in the intimate cockpit of the SJT, the performances will doubtless settle as the run proceeds. In the meantime, Saskia Butler's Emma is quite superbly understated and both Maeve Larkin as the aristocratic bird-watcher and Matthew Cottle's exasperatingly unthrusting Alistair are tellingly well pitched.

The SJT's continuing trawl through the Ayckbourn back-catalogue is clearly to the taste of its predominantly elderly, well-heeled audience. It's not the most forward-looking policy for a theatre in 2003, but at least it's done with some style and panache.

- Ian Watson