In 1944 Terence Rattigan wrote a play called Less Than Kind, but soon after was persuaded to revise it, and does so in Love in Idleness. Now Trevor Nunn has brilliantly synthesised the two versions.

The play is set in the last year of the Second World War and Eve Best's subtle, beyond-hilarious portrayal of Olivia, is the widow of a dentist in Barons Court, who has since been taken up and installed in the Westminster home of a war minister, a Canadian industrialist who just so happens to build tanks. So it's up in the world for Olivia, whose social manner appears to have been ready and waiting for her ascent.

Life throws a wobbly when she receives a wire saying that her only child Michael, who was 13 when she last saw him, has landed back in England after four years as an evacuee in Canada. Olivia is genuinely thrilled on one level; she's devoted to the boy. But he has no idea about her new menage – a fact that may severely complicate all those difficult adjustments she will have to make to the youth in that liminal state (“too old to spank and too young to punch on the nose” as the exasperated war minister puts it) who returns to this Elsinore-by-Thames.

We first find Best's Olivia in what for some would-be salonistes is the main activity of the day: head-hunting dinner guests. No one projects better than this actress the sense of a rich, tremulous hinterland that gives evidence of itself in hilarious, erratic lurches from under the gracious scattiness of the social self.

Forever raking his slick of jet black hair, young Edward Bluemel is perfection as the disaffected son playing Hamlet games. Sometimes he reminds you of William Brown trying to wind up his sister Ethel and her latest beau. Other times he reeks of a prim little lefty. Anthony Head is excellent as the Canadian industrialist – sounding like Conrad Black and presumably meant by Rattigan to evoke Beaverbrook. I was left in bits.

I saw Rattigan's original unproduced version of the piece, entitled Less Than Kind, when it first saw the light of day at the Jermyn Street Theatre a few years ago. The dramatist rewrote that draft, as it were, at the behest of the celebrated showbiz couple the Lunts. Rattigan had wanted to bring his Hamlet into real political opposition to the minister, accusing him of feathering his nest as a war-profiteer in a contest where principle (difficult to keep pure when you are only rising 18) is compromised by Oedipal jealousy. The Lunts persuaded Rattigan to lighten things and, now called Love In Idleness, that version received its West End premiere in 1944.