Twelfth Night is often called Shakespeare’s sunniest comedy, which is fine provided one remembers that the sun can burn and blister as well as warm. What’s impressive about Michael Grandage’s 1920s-era revival isn’t just the excellent acting, from Derek Jacobi and others, but the acknowledgement that, as romantic comedies go, the stakes are as high as the incidents are funny.

Last night the tone was set from the opening second, with Mark Bonnar’s half-naked Orsino rushing on to demand more music, as feverish as a pop fan terrified of missing Glastonbury.

The fervour of his love for Indira Varma’s elegant Olivia may seem odd, given that he ends up with Victoria Hamilton’s Viola, but then there’s something manic about his personality and always an intensity in the Illyrian air. You sense it in Hamilton herself, so agonised by the disguise forcing her to suppress her passion for Orsino that her very body gasps and gulps. You even sense it in the comic characters.

Has there ever been as snootily correct, as majestically prissy a steward as Jacobi? His first word, which is a simple “yes”, becomes a drawn-out sneer and ever afterwards his Malvolio is, at least in his own fancy, a Jeeves who is also a blend of Beau Brummell, Lord Chesterfield, Casanova and Napoleon. The scene in which he’s tricked by a fake letter often disappoints, but not here, with the humourless puritan practising a smile that starts upside down, becomes a lunatic gape, and ends up a clownish series of twisting lips.

Nor is he isolated in hilarity. Ron Cook’s sottish little Belch and Guy Henry’s dim, tapering Aguecheek make a terrific double-act, partly because they’re more unequal in size than the two Ronnies or, it sometimes seems, a pine and a thornbush. Henry exudes affability from the sky, while Cook catches his character’s earthiness and, at times, ugliness. It’s a pity that Grandage’s cuts, which also mean the omission of the character Fabian, include the aside in which Belch vows to filch Aguecheek’s horse; but, never mind, Cook still reconciles the comedy with an unsentimental picture of a mean and predatory drunk.

Jacobi manages much the same feat. So serenely censorious and primly conceited a man merits the punishment he duly receives, but he’s justifiably fierce, painfully furious in his final humiliation. The production ends happily, with a lovely new visual trick I won’t reveal — but also with another example of that intensity which is maybe its key strength.

Box office: 0844 4825120, to March 7 2009

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