Theatre: Responsible Other: an assured effort from newcomer Melanie Spencer; The Moment of Truth: Peter Ustinov fails to impress as a playwright

Dominic Cooke did it at the Royal Court. Now Ed Hall is having crack as well. Cooke’s crazy decision to place his theatre at the disposal of young scribblers prompted the emergence of several brilliant new female playwrights, some barely out of their teens. Ed Hall, following suit, has brought a play by newcomer Melanie Spencer into the Hampstead’s studio space downstairs.

Responsible Other is a relationship drama set in Northampton. Teenage Daisy has just lost her mum to cancer. And she’s afflicted by a rare condition, lupus, which damages the organs and prevents sufferers from venturing outdoors. Her best mate Alice tries to cheer her up with newsflashes from the classroom and romantic chitchat about fit young shelf-stackers at Sainsbury’s. Alice says she’s worried about becoming ‘chunks’ (fat) and hopes to ‘catch bulimia’ before seeing One Direction at the O2. They practise pronouncing ‘r’ in French. ‘More burpy. You got to say it like you’re literally going to be sick.’ Their dialogue crackles with wit, energy and warmth, and the emotional tensions between them are shrewdly observed.

Alice is desperate to alleviate Daisy’s sense of exile and yet both are aware that Alice is being tugged away from Daisy’s sickbed and towards the thrills and dangers of adolescence. Their friendship is acted with oodles of sassy charm by Alice Sykes as Daisy and Candassaie Liburd as Alice. Likewise, Daisy’s fraught but loving relationship with her widowed father is convincingly captured. They nag and fret at each other like an old married couple and Daisy feverishly scours his conversation for any hint of a romantic rival among his work colleagues.

These engaging, hard-edged relationships form the beating heart of the play. Elsewhere Spencer is less assured. She gives Daisy a fretting, dim-witted auntie who acts as chaperone during her trips to the lupus unit at St Thomas’s in London.