The big picture: Julie Christie and Dirk Bogarde film Darling, 1964

Julie Christie and Dirk Bogarde near Lord's cricket ground in London, between takes of John Schlesinger's film Darling, 29 September 1964. Photograph: Keystone-France

Photographs are time capsules, histories that compress information about more than the single moment when the shutter blinked. This one ranges across two centuries before settling on one charmed decade.

The water fountain, propped on a pedestal and topped by an officious obelisk, is a relic of Victorian philanthropy, catering to the thirst of the itinerant poor. The passing matrons could be Edwardian, wearing a genteel uniform – funereal hat and oppressively long coat, gloved hands and festoons of pearls round the neck – for a promenade to the shops. The young couple holding hands belong in a later, more relaxed era. She, idly dangling her bag from her hand rather than holding it protectively in front of her, wears a dress that could be by Mary Quant with a collar that makes her look like a sunflower. The old women are dressed for wintry old age; this sprightly pair – both with sunglasses, he with no tie and carrying a jacket he doesn't need – bask in the springtime of the body.

Time, like this north London thoroughfare, is a one-way street. The sun is behind all these people, and the shadows cast by bodies, slanting trees and the upright lamp-post are long. But the figure sitting down on the pavement, with a suppliant crouching beside her, is exempt from the flow; she has parked herself in a deckchair as if she were at the beach, not in a harried place of transit. For her it will always be 1965, and she will always – thanks to John Schlesinger's film – be beautiful.

The character played by Julie Christie in Darling is a go-getting model and sexual careerist; Dirk Bogarde is the television journalist who tracks her social rise. Almost 50 years later, the fable about vacuous, ephemeral celebrity remains tartly relevant. The photograph, however, is not satirical. Despite the Op Art glasses and the winklepicker shoes, Christie transcends fashion. Wearing a schoolboy's cap at a rakish angle while exhibiting – if you look very closely – a stocking top that marks the border beyond which the eye can't trespass, she also bestraddles the sexes. She bites her lip to signal a delicious, teasing indecision; Bogarde's bristling quiff alerts us to the urgency of his whispered appeal.

The overdressed frumps still plod through the dowdy, monochrome 1950s. But for me, Christie's shock of hair is as golden as the afternoon sun, her blazer dazzlingly candy-striped: in a black and white world, she radiates colour. Obelisks represent solar rays that were symbolically petrified, and the one at the kerb should be pointing its chiselled tip at her.