A trans-generational romance bracketed by two suicides may not seem ideal comedy material but 1971’s mainstream flop Harold and Maude became an unlikely cult movie, making ‘top 100’ lists after a 2012 DVD release.

This new stage version says more about modern attitudes to ageing, about feminism, migration and seizing opportunities than the current slew of angry fringe diatribes. And it says it more elegantly.

Sheila Hancock’s 79-year old aged-in-the-wood Maude teaches Bill Milner’s compulsively insecure 19-year old Harold a kind of Mindfulness: savour the orange, smell the coffee, seize the day, count the stars, climb trees, do what your heart wants rather than what society prescribes. But she delivers these homilies with a lightness of touch and a subtle sense of irony that makes even the trite ones palatable.  And one or two of her existential observations may just make you think.

Director Thom Southerland has framed the production as a surrealist painting – and the details in Francis O’Connor’s set are meticulous: the distorted perspective, the ladder to nowhere, the clouds, the perfectly-posed still-life positions of the actor-musicians propping up their instruments are taken straight from Magritte or Dali. Both the visual staging, and some charming music by Michael Bruce give what could have been a lightly gruesome comedy a third dimension of pure class.

You could argue there’s a growing cinema genre of ‘take your gran’ movies – all those Real Marigold, Quartet, feisty old dames not going quietly but still getting laid sagas with Dame Judi or Imelda Staunton or Celia Imrie … so maybe this is a zeitgeisty theatrical equivalent: a late-flourishing romance but refreshingly without their glucose coating.

I liked it: both leading performances are soundly observed, but the slightly batty slightly surreal production most perfectly surrounds what Hancock has done with her character. Although an American septuagenarian, she doesn’t need to be wisecracking every third line like The Golden Girls and the gentle Austrian accent works best when she opens her Viennese suitcase of memories from her colourful and painful past.

Apart from a clunky portrayal of Harold’s ghastly mother in an equally ghastly acrylic wig, the ensemble is first-rate, but the scene-stealer is Samuel Townsend’s accordion-playing policeman who also impersonates the barking seal Maude purloins from an inattentive zoo.

Comedy gold. We were, incidentally, doing seal barks on the way to the tube … now that‘s better than coming out humming the theme from Kinky Boots.