Red Joan: Judi Dench should have defected from half-baked spy drama

Trevor Nunn's cinematic career has – let us put this politely – failed to generate the same acclaim as his work for the theatre. It's more than 30 years since he directed Helena Bonham Carter in a famously narcoleptic study of Lady Jane Grey. A decade after that, he delivered a mechanical take on Twelfth Night that smelt so strongly of greasepaint that one needed a little lie down afterwards. It's taken another 20 to rope Judi Dench, an old collaborator, into a film that deserves note for all the wrong reasons.

It takes a quality – not a gift exactly, but a quality – to make something so boring of such a fascinating subject. Adapted from a novel by Jennie Rooney, Red Joan gestures towards the true story of the Soviet spy Melita Norwood.

The film begins with elderly Joan Stanley (Dench) opening the door to police officers who reveal that, following the death of a diplomat, she is to be charged with leaking atomic secrets to the Russians in the years after the second World War. We then flash back to wartime Cambridge (where else?) and follow her dalliance with communists, her early work on the British bomb and her eventual decision to assist the KGB.

Cardigans worn in dusty common rooms. Documents passed in darkened corridors. Clement Attlee getting to steal Ernie Bevin's line about putting "a Union Jack" on the A-Bomb. You're pushing at an open door with this critic, Trev. Sadly, it just doesn't happen.

Dench, who appears only fleetingly between two bookends in the year 2000, tries her absolute best with dialogue that barely merits the word "functional". Her argument that she passed secrets out of fairness rather than political conviction is an interesting one. But the film is dead as dust at its period core. Sophie Cookson plays the young Joan as a prim miss with a tedious line in prudish furrows. Early on she meets up with some glamorous Europeans and is taken to a communist meeting that breaks new ground in cliched representation, with verses from the Red Flag followed by a screening of Battleship Potemkin.  They, at least, got to watch a great film. The rest of us are stuck with this.

Tom Hughes is okay as the dashing Leo. Tereza Srbova hugely overdoes the mysterious vowels as the deadly Sonya (who tragically is never referred to as "Red Sonya"). Think of the subversives as the "darling" comrades so beloved of Linda in Nancy Mitford's The Pursuit of Love and the long minutes may crawl a little less slowly. If you can't manage that, you'll be saddled with a tedious trudge towards an already determined conclusion.

A wasted opportunity.

Opens April 19th