The House of Commons is described in Terence Rattigan’s superb drama as a place of too little ventilation and too much hot air. There’s also a view expressed that when the day dawns where small matters of justice – a fair trial for a teenage boy accused of stealing a five shilling postal order and expelled from college – are too small to be counted important, then democracy at large is no longer safe.

These remarks always raise a laugh but, in the current climate of outrage over MPs’ expenses and wholesale fraud, Rattigan’s moral decency as a playwright of public affairs is resoundingly renewed. And Stephen Unwin’s sedate but clearly pointed production hits home hard.

The legal case on which Rattigan based his drama occurred in 1908. His play, first performed at the end of the Second World War, is set in the afterglow of the Edwardian age on the brink of the First.

Thus it embraces, in the fall-out from Ronnie Winslow’s expulsion from Osborne Naval College, ideas of justice, the emancipation of women (Ronnie’s sister Catherine is a firebrand suffragist), the intrusion of the media, the onset of hardship, and the melting of class barriers.

At the centre is the determination of the paterfamilias, retired banker Arthur Winslow (Timothy West, in nicely sarcastic form), to clear the family name by hiring the star barrister of the day, Sir Robert Morton. Adrian Lukis enters on this great role like an unduly smirking Dracula, but settles into a steely theatricality, while Catherine (Claire Cox) stifles her distaste for his “establishment” credentials and ponders her own impending dull marriage to the scion of a military family (John Sackville).

The cast-iron construction allows plenty of room for Diane Fletcher, as Ronnie’s mother, to preside over mounting misery with soignée affability as Arthur’s health tragically deteriorates. Is the price of justice worth the agony, especially as Ronnie adjusts happily to his new school?

Designer Simon Higlett provides a handsome, cream panelled Kensington drawing room. Ronnie is not too simperingly played by Hugh Wyld, and there are pleasing cameos from Sarah Flind as the maid and Roger May as a squashed solicitor. It’s clearly, in the end, Catherine’s play, but everyone has a good shout: The Winslow Boy is woven into the very fabric of English life. It’s a modern classic.

- Michael Coveney