ALAN Bennett's new play at the Lyttelton. The Madness of George III, is about what its title suggests. It offers -no hidden, agenda or coded thesis and, unlike Nick Dear's Georgian monologue In The Ruins, it waves no republican banner. It is basically a highly intelligent history-play about the sad, dubiously mad Hanoverian Lear.

If I have any reservation, it is that it lacks the resonance of metaphor. Goethe once said that a play should be symbolic: each bit of the action must be. significant in itself and point to something still more important behind it. Mr Bennett makes any number of astute points about the assertive ignorance of doctors, the inbred opportunism of politicians and the relativity of definitions of madness. But he never achieves the universality that is the prerequisite of great drama.

What Mr Bennett does do is to touch our hearts and tickle our intellects. He sets the action in 1788-89 by which time George III had been enthroned for 28 years, conceived 15 children and contrived to lose the American colonies. The mere mention of the last sends the monarch into a shuddering rage; but when regal nonconformities acquire the symptoms of madness, including the unstoppable flow of streams of consciousness, the vultures start to gather.

With needle-point skill, Mr Bennett shows how everyone has a vested interest in the king's condition. Pitt, the . beleaguered Prime Minister, needs to preserve the image of the king's sanity since he governs by the monarch's consent The debt-ridden, dissipated Prince of Wales, aided by the power-hungry Charles James Fox, equally needs to establish George's madness to be proclaimed Regent. Meanwhile doctors; jealous of their own status, quarrel amongst themselves like Moliere quacks, variously diagnosing flying gout, creeping palsy and galloping constipation.

Mr Bennett unravels the political intricacies of the period with Stracheyesque wit. But at the heart of the play lie scenes of horrific pathos showing the curative techniques of Francis Willis who ran a private Lincolnshire madhouse. Willis's method was total mastery of the patient; and to that end we see the king strapped in a restraining chair, bound in a straitjacket and even gagged to silence his scatological ramblings. But, instead of scoring easy points off Willis's stick-and-carrot methods, Bennett shows how his puritan domination achieved a temporary restoration of the king's stability.

Through the action Bennett raises all kinds of fascinating ideas: the kinship between monarchy and lunacy, the therapeutic value of art as George discovers an image of his predicament in King Lear, the connection between lies, tricks and scams and constitutional stability. Bennett also preserves a miraculous hairline balance between tragedy and comedy: he makes the king's plight profoundly moving while nonchalantly throwing off Wildean lines like "The asylums of this country are full of the sound of mind disinherited by the out of pocket." But if the play knocks at the door of greatness without quite gaining admission, it is because it lacks the single controlling idea that elevates a case-history into myth.

Mr Bennett, however, forces you to judge him by the highest standards. He also created in the "mad" king, (later found to be suffering from porphyria, a disorder of the metabolism) one of the richest roles in post-war drama superlatively played by Nigel Hawthorne. We knew Mr Hawthorne to be a deft comedian but he here gives us the king's tyrannical humours, surreal babblings, unconscious desires and helpless vulnerability. But the genius of the performance lies in the suggestion that under the status-conscious monarch who enjoys stately Handelian entrances lies a prosaic, domesticated man who likes nothing better than to curl up with "Mrs King."

The play is also beautifully served by Nicholas Hytner's production which combines, classical clarity with filmic speed as scene melts into scene with the aid of Mark Thompson's Brechtian traverse curtains. In a large cast there are also rich, Gillrayesque performances from Harold Innocent as the king's bumbling physician, from Charles Kay as the steely Lincolnshire specialist and from Cyril Shaps as a the medical obsessive who leaves no stool unturned. Julian Wadham also endows the young Pitt with just the right mix of moral rectitude and ruthless ambition.

It is, in every sense, a big experience: an engrossing exploration of Byzantine Georgian politics and the insulated despair of derangement. Posterity will judge whether the play makes history but it certainly records it with Bennett's unique intuitive flair.