Sophie Khan Levy
Sophie Khan Levy in Hanna
© Robert Workman

Nature or nurture? Sam Potter's new play for Papatango explores what happens to two children – and their mothers – when they are accidentally switched at birth. It's a scenario to dread – how does one deal with the idea that the child you have been bringing up as your own, isn't in fact the one that you thought you had been growing in your womb for last nine months?

Though it does happen, it happens rarely and one of the things to applaud about Potter's play is that despite a slightly sensational subject, Hanna deals carefully and intelligently with real, pertinent issues of class, care, family and love.

Hanna is a mum; a bright young woman who talks out to us as if she is explaining the whole story from start to finish to a journalist or social worker. It wasn't an easy birth, she explains, and she was knackered. So when her baby was taken away for treatment for jaundice and brought back again, she barely notices the difference. It's only much later, after her partner Pete doesn't believe their daughter Ellie is really his and demands a paternity test, that they discover what has happened. From then it's Hanna's job - alone after Pete has left - to connect to the other family, who have her birth child and who, in comparison to her, are exorbitantly rich. The guilt she feels, about not noticing, about what she can offer Ellie, about her 'real' daughter, is palpable.

The monologue twists and turns, building to a climax which feels a step too far, but along the way Potter weaves a believable, relatable voice. The rhythm of her speech means Hanna feels like she could be your next door neighbour, your best friend, maybe even you.

This is helped in no small way by the performance of Sophie Khan Levy who is superb as Hanna. She fidgets, pulls on her sleeve, smiles coyly or shakes her head at some of her mistakes. She is a flawed, self-conscious human, someone visibly struggling to work with the cards they have been dealt. But her strength and her love for Ellie never wavers and for all her unsurety she emerges a tower of strength.

It feels a little as though Potter couldn't work out where to go with the story and as a result the final third of the piece is forced. There are also clunky moments of exposition which lay bare the central premise as an improbable one.

Still, this is a vivid 90 minutes which manages to tell a solid, engaging tale on all the terrors, complexities and joys of being a mother.

Hanna runs at the Arcola Theatre until 20 January.