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. Auntie No-Brain befriends a saintly Ghanaian nurse and they sit on the Embankment together, staring inanely at Parliament, and making sweetly naive comments about their lives, while exchanging niblets and recipes for ‘pounded yam’. Quite how this improbable sugar-coated alliance earned its place in the play is hard to ascertain. My guess is that Spencer liked the idea of a saddo from the sticks being schooled in the delights of multiculturalism by one of its supreme exponents: a wise, benevolent African mother who works for the NHS.

The play’s composition is a little untidy and Spencer wastes precious resources by giving a terrific actress, Danielle Bux, a tedious walk-on role as a deadly earnest maths teacher. Spencer’s facile desire to make us like the characters by making them like each other is a policy that will deliver diminishing returns. Otherwise, this is a tremendously assured effort and Spencer directs her own work with maturity and aplomb.

Southwark Playhouse offers the juicy prospect of a neglected play by Peter Ustinov on the subject of military diplomacy. Ustinov was supremely clever, witty and sophisticated but when he slotted the foolscap into the typewriter his brains seem to have trickled into the gaps between the keys. A bewildering naivety afflicts this play. Ustinov introduces us to a tinpot dictatorship in the aftermath of a brutal defeat and he asks us to believe that its leaders might remain in power without sparking a popular revolt. Given that he lived through most of the 20th century, this seems an absurd fantasy to entertain.

Even sillier, he shows us the vanquished leaders dictating terms to their conquerors. Admittedly, his target isn’t political wrangling so much as the psychology of dictatorship and he wants to satirise militarism by introducing us to a doddery old field marshal who emerges from retirement to rescue his benighted people. Ustinov is on to something here. A bruised and exhausted state will sometimes invite an ancient war hero to perform a final act of patriotism. Von Hindenburg, aged 78, served as Weimar president. Marshal Pétain led Vichy France. And in the 1950s, Britain elected Churchill who was far too old and sick to act effectively as prime minister. (We should have left him on Onassis’s yacht with his cigars and his Special Brew.)

Ustinov the playwright is the victim of his own virtues. He has read too many plays. And his wide researches have left him scant room for experimentation and originality. He relies on Shaw for the overlong and flashy speeches that pepper the drama. And he summons up Shakespeare for the passages of sentimental tragedy towards the end where the bumbling has-been suffers an ignominious yet somehow uplifting mental collapse while his sorrowing daughter spouts many a gobbet of tear-stricken lamentation. The cast, led by Rodney Bewes, give it all they can. But Ustinov has given them far too little in the first place.