Fourteen years have passed since Jonathan Lewis's fine debut play Our Boys opened at the alas no more Cockpit Theatre, but my recollections of one scene are as vivid as ever - a group of convalescing squaddies passing time by playing “The Beer Hunter”, a fiendish spin on Russian Roulette with agitated ale cans standing in for the more traditional revolver. Much as I enjoyed his latest effort, though - co-written, like his first work, with his wife Miranda Foster – I doubt that it will stay with me beyond the end of next week.

This has less to do with a gifted five-strong cast and Lewis' sprightly direction than the weirdly inconsequential subject matter. No doubt there is a terrific comedy to be forged from the plight of cash-starved voice-over artistes in modern-day Soho, but All Mouth isn't it; nor do Lewis and Foster convince us these tonsils-for-hire are part of a heroic dying breed, on the verge of being swept away by computerised facsimiles and "robot movie stars".

It also strains credulity that such a mismatched quartet as doddery old ham Digby (Christopher Benjamin), divorced mother-of-two Mel (Caroline Harker), pedantic milquetoast Paddy (Simon Chandler) and brash egotist Greg (Nigel Whitmey) would share the same planet, let alone the central London flat that serves as their makeshift joint office.

A tenuous situation is made shakier still by an off-stage strike ballot that threatens to put them on opposite sides of a picket line and by Digby's forthcoming appearance on Desert Island Discs, a running gag that gives the writers free rein to pepper the action with confessional monologues aimed at an invisible Kirsty Young.

A more interesting note is sounded by the arrival of Rod (James Russell), an Ortonesque interloper who wheedles his way into this insular unit by seducing both Digby and Mel in quick succession, then nabbing the plum role in EastEnders Greg had set his heart on. This intriguing sub-plot, alas, is left as frustratingly underdeveloped as Digby's recent gay-bashing at the hands of a violent one-night stand, or Paddy hiding his true calling from his family in the suburbs.

All Mouth's most entertaining moments all take place in the recording booth artfully hidden behind the transparent back wall of Anthony Lamble's set - Harker gamely trying to satisfy a control room full of testy washing-powder executives, for example, or faking an orgasm as she and her colleagues dub some dodgy Euro-porn. Pity that Lewis and Foster can't provide a satisfying climax themselves, their open-ended conclusion feeling as unrealised as everything else in this fitfully amusing but dramatically hollow piece. Who'd have thought that characters who spend their lives behind a microphone would have so little to say?

- Neil Smith