The Madness of George III Theatre Royal Bath Alan Bennett’s extraordinarily powerful drama is the final production of this year’s Peter Hall season.

David Haig in the title role is a tour de force, sane or mad. His subtle skills keep the drama on course during a slightly erratic first half in which the comedy veers dangerously close to pantomime.

One half expects the high wigged and rotund Prince of Wales, as played by Christopher Keegan, with a squeaky voice, to break out the custard pies, so frivolous is his manner.

Nicholas Rowe’s straight-laced William Pitt however, also generates a good measure of gravitas to anchor the drama. And despite the coldness of the character Rowe inspires some empathy.

There is a great deal of intelligent comedy - this is Alan Bennett after all - and much of it at the expense of the medical profession, which in the 18th century was both primitive and often more life-threatening than the illness.

There are harrowing passages as the hapless King is bled and blistered and fed dreadful potions, tied to a chair or constrained in a straight-jacket, each according to the whims of the four doctors who attended him.

David Haig had us all wincing.

He presented two very different personas. The brisk and hearty well King, full of 'what-whats' and 'hey-heys' and the erratic, abusive and foul-mouthed sick man.

His recovery was more due to his own constitution than the ministrations of any of his physicians.

Porphyria, the hereditary illness from which he is believed to have suffered, was unidentified at that time.

But Bennett takes a malicious delight in letting the physicians expose their ignorance in way which produces a collective sharp intake of breath from today’s audience.

There are rich performances from Beatie Edney as Queen Charlotte, Orlando James as the King’s kindly equerry and Charlotte Asprey as Lady Pembroke, the Queen’s lady–in-waiting.

But this is also ensemble playing at its best. You have until September 3 to catch it.