POP / A belated Serge of interest: The French adore anything about Serge Gainsbourg, Jane Birkin included. We failed to see the light. So Birkin is back, holding his torch

As retirements go, Jane Birkin's has been mercifully short. Just over two years ago I saw her 'farewell performance' at the Francofolies Festival in western France, an emotional affair with screams, bouquets and palpable adoration emanating from a 6,000-strong audience entranced by the shy figure in jeans, T-shirt and tumbling brown hair. All the songs were by her Svengali and one-time lover, Serge Gainsbourg, who had died 15 months earlier.

'I'd like to talk about him,' she said, voice breaking, in a rare aside, 'I thought it would be easier later, but it's not true . . .' Her finale, the haunting 'Je Suis Venu te Dire Que Je m'en Vais' (I've Come to Tell You I'm Leaving), was enough to test the rigidity of the most Novocained and uncomprehendingly Anglo-Saxon of upper lips.

Afterwards at a press conference, a vulnerable and distracted-looking Birkin, still in jeans and tennis shoes, explained she was tired of singing after a long tour and just wanted to do something different. 'I wish I could have sung Serge's songs in England, though,' she said. 'I've tried but no one was interested. I'd have sung anywhere - for small audiences, little money, at the Pizza on the Park . . . it was his greatest wish to be known in England. It seems so unfair.'

On Sunday, Birkin makes her British singing debut at the Savoy Theatre, where her mother, the actress Judy Campbell, performed with Noel Coward in Relative Values 40 years ago. The concert was instigated by her 'oldest friend', Gabrielle Crawford, ex-wife of the actor Michael Crawford - they all met in 1965 on the set of The Knack, Birkin's first film - as part of a series of events to raise money for a cancer-scanning machine for the Royal Free Hospital, Hampstead (where Gabrielle Crawford's brother is a surgeon).

Keen to help the charity and, even more, to evangelise for the Gainsbourg oeuvre, Birkin is open to the press, and unsecretive by the standards of a major star, which she is in France. Rambling answering machine messages chronicle her perambulations around Paris - 'I've gone to the printers - back at 5'. . . 'Gone to the Bruel concert with Lou. Back at midnight. Please, please leave your number . . . message after the fax, er, I mean the beep thing. . .'

Run to earth 'cooking the dog's lunch', Birkin launches into a telephonic stream of consciousness, much of it concerned with Gainsbourg: the previous night's concert by the pop star Patrick Bruel, who sang Gainsbourg's 'La Javanaise' as a homage, inspiring 17,000 people to light their briquette things and sing along; Gainsbourg's love for England, from the studios where he always recorded, to the breakfasts of his musical director Alan Parker's mother; Gainsbourg's enduring appeal to the young. He was 62 when he died, yet his Montparnasse grave and Left Bank house are bedecked with the messages and gifts of his fans ('Wait Serge, we're coming to join you' is a common theme). It's important to note that none of this is the least exaggerated, not that Birkin's anxious, truthful voice would make you suspect it might be. Serge Gainsbourg still exerts a magnetic hold on the French imagination, and on cult followings around the world. And his prodigious contribution to Franglais should have been enough to give the entire Academie Francaise a collective crise cardiaque ('Je suis tombe sur les cops. . . ils ont cherche mon spliff. . . Je flippe. . . c'est pas mon genre de trip' from his 1980 'Brigade des Stups' - Drug Squad).

Gainsbourg, born Lucien Ginsburg, the son of a Russian Jewish cabaret pianist, started his career in Left Bank cabarets in the late Fifties - the surrealist dandy Boris Vian was his role model - and had recently made a successful transition to pop / rock when he met Birkin in 1969. His songs were much in demand and a key clientele was young, female, beautiful, often from an acting background: Bardot, Deneuve, Darc and Adjani are all Gainsbourg interpretes. He had already had the demure teenage star France Gall raising temperatures with his ode to the pleasures of sucking lollipops and was nurturing the character of bohemian seducer that later so fascinated the public.

Jane Birkin must have seemed like a personal gift from Dionysus - not to mention Binkie Beaumont, the legendary London agent who first spotted her - when she fell in love with Gainsbourg on the set of the film Slogan. Aged 22 and married to the composer John Barry, she was an irresistible combination of Miss Ironside's School, Kensington, where she was educated until her stage debut with Sir Ralph Richardson at age 17, and Swinging London, which she had penetrated effortlessly in three films, notably Antonioni's Blowup, and two plays.

During the 13 years they lived together, and later after a brief estrangement, she was his Muse and most important interpreter. Gainsbourg taught her to sing in the same breathy, artless, unrehearsed way he preferred with all his protegees. 'It was a point of principle with him to be spontaneous. . . he'd stay up all night writing songs and give them to you at the last minute.'

Their first collaboration was the heavy- breathing classic and succes de scandale 'Je t'aime moi non plus', which Gainsbourg had already recorded with Bardot, who subsequently refused to have it released. Birkin accepted the job with alacrity - 'I didn't want Serge recording that song again with someone stunning like Mireille Darc.' The success of 'Je t'aime' launched Birkin's career in France, where she has recently added serious theatre (five productions since 1985) to her 15 records and dozens of films, the most recent as writer / director.

Is her renewed zeal to make Gainsbourg known in England a way of posthumously repaying what he did for her in France? 'Maybe. . . I hadn't quite thought of it that way. . . but it's also that I feel it's almost like being ungrateful not to sing Serge's songs. He wrote some of his most beautiful songs for me, and he knew they were extraordinary - if I sang other songs he'd say 'But why? I've written you so many'.'

She is under no illusions as to the ease of the task, however. For all their melodic catchiness and stylistic variety - he moved smoothly and distinctively with the times - Gainsbourg's complex songs need a good command of the French language and culture to appreciate fully. 'Je t'aime moi non plus' is a case in point. The title is based on a quote by Salvador Dali: 'Picasso is Spanish - so am I; Picasso is a genius - so am I; Picasso is a Communist - moi non plus (neither am I).' 'Serge and I tried to translate it,' Birkin says, 'But you just can't. I love you, neither do I is ridiculous. . . still, I think there's a new curiosity about French things in general. My only sadness in all this is when I think merde]. . . he's not around here to see it.'

Jane Birkin - A Tribute to Serge Gainsbourg; 7.30pm, Sunday 25 September, Savoy Theatre (Box-office: 071-836-8888)