I worry about two things in relation to Simon Stone's modernised, almost unbearably powerful reinvention of Lorca's 1938 play. The first is the impact on its star performer Billie Piper. She plays not the title role here, a name which Stone could have easily ditched so complete is his reworking of the Spanish original, but a woman in the programme named as "Her" who, as with Lorca's original creation, becomes defined by the need to have a child.

By the end of this production's uninterrupted one hour, 50 minutes, Piper appears to be emotionally and physically drained to an almost dangerous degree. On this night, her bows and gestures were made semi-consciously, it seemed. Her eyes were unfocused and her body appeared to be moving by muscle memory alone. It took a while for a smile to finally play over her lips as the applause continued. Eight performances a week.

My second worry is for anyone in the audience who has attempted to have a child and has either failed or not yet succeeded. As brilliant as this show is, I'd hesitate before recommending it to them. It could be too painful.

For his directorial UK debut, Australian-born Stone has a created a forensic examination of the pressures that come with wanting a baby. The couple here are not Lorca's farmers but urban and urbane Londoners. Aussie John (Brendan Cowell) and his English partner (Piper) have bought a house and we first encounter the couple in the giddy, champagne-fuelled optimism for the future. She, a journalist, suggests that it would be great to have a child. He, whose job entails travelling around the world a lot, agrees. Thereafter, Stone's episodic, naturalistic script keys into the conversations and pressures that many a couple have had as they attempt to balance the time it takes to work and procreate.

In other respects, the play stays pretty loyal to Lorca's time-jumping structure, and also to the series of events that ratchet up the pressure to conceive. Elsewhere, people have babies with ease.

Adding to the sense of being trapped by circumstance is the production's design by Lizzie Clachan. It's a promenade piece with the action taking place behind glass walls, which means the cast have to wear microphones so that their voices and the echoey acoustics of the space in which the play is performed can be heard via speakers. So, aside from the metaphoric significance of seeing a couple hemmed in like observed rats in a lab, the production evokes a kind of voyeuristic fascination.

As Her bloke, Cowell delivers a brilliantly judged portrayal of a modern, well- meaning metrosexual whose masculinity becomes a barrier to understanding his partner's torment. But, with Piper, you get the sense that this is the performance to which her previous excellent appearances on stage have been leading. She's one of those rare actresses who can be monumentally tragic and almost casually realistic at the same time. She charts an exhausting yet mesmerising descent into childless madness.

But the above warning is not just for those without children. The couple's descent from trust to estrangement is terrifyingly convincing. Even for those much closer to happiness it's impossible to watch without a sense of "there but for the grace of God go I".