Uprooting yourself in order to settle down a few yards from supposedly close friends in the rural outback is always a risky endeavour. For the writers Katherine Mansfield and Middleton Murry, such a move verged on the cataclysmic.

Their neighbours in Cornwall during the First World War were D.H. Lawrence and his German wife, Frieda. Had such measures been available in 1916, poor Murry and Mansfield couldn't have been blamed if they had petitioned the St Ives authorities for a series of ASBOs.

Or so Amy Rosenthal suggests in her hugely diverting On the Rocks: a title that refers both to the landscape and to a friendship that is clearly imperilled from the moment Ed Stoppard's Lawrence lures Mansfield and Murry to the village of Zennor, assuring them that they are “our real and permanent blood-kin”.

For what can this mean for them? Having to watch sadomasochistic battles that begin with violence and end with sex on the floor. Being oppressed with excessive attention, then insulted as “worms” and “bugs” when they show any independence. And, worst of all, being bombarded with patronising homilies about Life with a big Lawrentian L. We would probably accuse Rosenthal of a weakness for sententious dialogue if anyone but Lawrence were her protagonist. But it's only too plausible that this self-obsessed control freak - for that's what the great novelist was - would order a friend to make himself “separate, hard and gem-like”, or describe his own put-upon wife as “all-devouring, monstrous, suffocating, the great annihilator”.

Indeed, one of the evening's pleasures is observing as Stoppard's Lawrence - earnestly, eagerly and unstoppably - exposes his own arrogance by imposing definitions of honesty and friendship on chums too intimidated to resist.

Charlotte Emmerson, who plays Mansfield, could go farther in showing the blocked short-story writer's depression and despair. And Nick Caldecott's Murry is too obviously the wanly intellectual antithesis of Stoppard's Lawrence.

Yet this produces some hilarious moments, notably when the rampaging novelist inveigles the repressed essayist into a wrestling match that's a bit less naked, but even sillier, than the one he was to celebrate in the book he is writing during the play, Women in Love.

And I also laughed a lot at the ironies Rosenthal draws out, including Lawrence's ferocious attacks on the Bloomsbury set for failing to fight or stop a war from which he's even more withdrawn.

There are also fine performances from Tracy-Ann Oberman as a gloriously sensual, blowsily defiant Frieda and, in particular, the scrawny and intense Stoppard. Somehow he generates a little sympathy as well as laughter as he plays the cultural pirate king: bossing his crew, chasing his wife with a broken bottle, rhapsodising over Cornwall's fauna and flora, fiercely philosophising, and generally being, well, D.H. Lawrence.

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