THE NAME of the lyricist and composer Julian Slade will always be linked to Salad Days, the musical he co-wrote in 1954 with the actress Dorothy Reynolds as an end-of-season show for the Bristol Old Vic.

The previous year they had enjoyed a modest success with Christmas in King Street (the theatre’s address), and he had since become the company’s musical director. Now he and Miss Reynolds, 17 years his senior, had six weeks to create a successor and, so the story goes, were at a loss for a theme until a letter arrived from his younger brother, Adrian.

Having just left school, Adrian was being urged to visit their various uncles for advice on a career. One strand of the future musical was now in place. The source for the other, a magical piano that made everyone dance, is lost in time but it added the element of good-natured fantasy that breezed through the musical and caught the theatre-going public’s fancy.

The story was set in London during a heat wave and followed a young couple who have just left university and are beset by parents wanting her to marry well and him to find a decent career. Instead, they decide to marry each other and, between visits to his numerous uncles, look after an old street piano for a month, soon discovering its magically infectious power – Oh, look at me! I’m dancing! I’m going on one foot instead of on two – It isn’t a thing I’m accustomed to do . . .

Soon everyone within earshot of the piano’s catchy rhythm is joyfully leaping around; street urchins, civil servants, even bishops, abandon themselves to merriment until a government minister (another uncle) intervenes, only to be outwitted by the pilot of a flying saucer (yet another).

Certainly, this was a primitive structure for a show, devised for the particular talents of the Bristol company available to Slade at the time. But his catchy, clever and sweet-hearted songs proved irresistible. His melodies possessed that rare and blessed quality of showing themselves unforgettable after a single hearing. The lyrics too — simply rhymed colloquial phrases fitted the musical line so easily that words stayed in the memory along with tune.

After its three-week run in Bristol the show transferred to the Vaudeville Theatre in London, where it ran for five and a half years, overtaking Chu Chin Chow, The Boy Friend and My Fair Lady to become the longest-running musical (2,288 performances) in the history of the British theatre, a record it held until overtaken by Lionel Bart’s Oliver! a decade later.

Slade was just 24 when his musical hit the West End. Some critics sniffed at what they perceived as middle-class cosiness, unable or unwilling to recognise the gentle mockery that suffused the show. The original cast recording reveals that the young heroine’s voice was terribly, terribly pure, and the young hero frightfully, frightfully shy and manly – “Oh, Jane will it help if I marry you? Only if it will help.” Irony was an essential spice.

The success made Slade rich — and hugely benefited the Bristol Old Vic Theatre — and though several subsequent musicals reached the West End none came remotely near it in popularity. Free as Air followed in 1957, then Follow that Girl (1960) and a decade later Trelawny (1972). This last, starring Ian Richardson, Hayley Mills and Timothy West, opened the week before Jesus Christ Superstar, but Slade’s characteristic style of writing had already fallen out of fashion.

Julian Penkivil Slade was born in 1930 into an eminent legal family. His father, George, was a KC, and his elder brother, Christopher, became a Lord of Appeal. His mother, born Mary Carnegie, was left a widow when Julian was 12 but he won a scholarship to Eton and went from there to Trinity College, Cambridge, where the ability to write tuneful songs, already in evidence when he was a boy, resulted in an undergraduate musical for May Week, called Lady May, and another, intriguingly titled Bang Goes the Meringue.

He had ambitions to be an actor and, when Cambridge Shakespeare was still all-male, played Lady Macbeth to John Barton’s Macbeth. From Cambridge he went straight to Bristol, to be a spear-carrier, but within a year Denis Carey, then running the Old Vic, assembled the company and asked those who thought they could write a Christmas musical to raise their hands. Slade and Dorothy Reynolds did so and from that moment the trajectory of his career was set.

After Trelawny he continued to write, and throughout the 1970s his score for the Christmas Winnie the Pooh was heard annually at the Phoenix. He wrote for television, for the Open Air Theatre in Regent’s Park, and in 1991 Nutmeg and Ginger, his musical adaptation of the Jacobean comedy The Knight of the Burning Pestle, was produced at the Orange Tree, Richmond, although almost 30 years after its Cheltenham premiere.

By this time he had moved to London, to a garden flat in Chelsea where, over the years, theatrical mementoes came to cover the walls, and what space remained was occupied by his own drawings.

He sometimes spoke of his regret that so much of what he had written since Salad Days remained unperformed but sorrow never seemed to blight his relish for life, cinema, theatre and the company of his numerous friends and young relatives.

Salad Days is still given a London revival every dozen years or so — its most recent was in 1996 — and the magic piano is now displayed in the Theatre Museum. Like Sandy Wilson’s The Boy Friend, which began its long London run in the same year, its portrait of an unrealistically innocent world is made memorable by its wit and enchanting melodies.

Julian Slade, lyricist and composer, was born on May 28, 1930. He died on June 17, 2006, aged 76.