One of the finest motorcycle racers of his generation, Barry Sheene was 500cc world champion in 1976 and 1977. He was also highly regarded in this most dangerous of sports as a leader who championed riders’ interests against the dictates of the governing body, the Fédération Internationale de Motocyclisme (FIM).

Adored by his fans for his Cockney cheek, infectious grin and irreverent attitude to officialdom, he responded to them in return, and loved to wander among the crowds of spectators at trackside after a race. He was for some time the riders’ representative — and a fiercely outspoken one — on the FIM, and his hatred of its bureaucracy was legendary.

His care for other riders on the track earned him much affection among his peers. When, during a practice session for the 1976 Swedish Grand Prix, John Williams came off his Suzuki, Sheene swerved round him, screeched to a halt and ran back to the stricken racer, who lay choking with two men standing over him not knowing what to do. In a trice Sheene had Williams’s helmet off and cleared his airway. This prompt first aid undoubtedly saved Williams’s life.

Sheene campaigned vigorously against several circuits which he and many other riders considered dangerous, notably the Austrian Grand Prix circuit, the Salzburgring, after one rider was killed and four others were seriously injured there in 1977. But his most signal achievement in that sphere was to have the Isle of Man TT taken off the list of world championship events, after the circuit had claimed more than a hundred lives.

Between 1975 and 1982 Sheene won more international 500cc and 750cc titles than any other rider. Yet his playboy lifestyle, his dramatic crashes and horrific injuries made him almost as famous with the public as his victories did. The X-ray picture of his shattered legs, screwed together like a Meccano set by the surgeon Michael Cobb after a 160mph crash at Silverstone in July 1982, was flashed round the world and became one of the enduring images of motorsport.

Barry Sheene was born in Holborn, London, in 1950, the son of an engineer who was a motorbike fanatic. His uncle was a speedway rider. He first sat on a motorcycle at the age of two and was given his first machine — a 50cc Ducati four-stroke — at five. He was educated at St Martin-in-the-Fields School, where, as a persistent truant and rebel, he became intimately acquainted with the slipper and the cane.

On one occasion he retaliated against the school regime by nipping into the headmaster’s study, pinching the entire stock of instruments of chastisement from the cupboard and pushing them into the furnace of the school boiler. It was obvious that he and formal education had little to offer each other, and he left St Martin-in-the-Fields to sell second-hand cars. Later he was a courier for an advertising agency. In his spare time he raced motorcycles and in 1968 rode his first competitive race at the age of 17, a 125cc event at Brands Hatch — where his engine seized and he was thrown off.

Within a year he had won his first British 750cc championship, and he repeated the feat in 1970. The international stage was at that time dominated by Giacomo Agostini, who had ruled the roost since the mid-1960s and was to go on to win a record eight world 500cc world titles between 1966 and 1975.

Sheene came remarkably close to winning the world title in 1971. But at that time he was competing as a private entrant, and doing his own engine development against works teams with batteries of mechanics. In 1973 he signed up with Suzuki. Sheene won the European 750cc title in 1973, and in 1976 ended what had by then become known as the “Ago era” by winning the first of his two 500cc championships on a Suzuki. So complete was his supremacy that he had the title in his pocket after only five of the 12 races. He then refused to participate in the remaining seven, declaring many of the circuits to be too dangerous.

He was to land the title for Suzuki for a second time the following year, and was appointed MBE in 1978.

But at the end of the 1978 season he was beaten to the title by the American Kenny Roberts, who was to dominate the championship for the next three years. In 1979, too, Sheene had to be content with second place to Roberts, with whom he fought a memorable duel at Silverstone. Leaving the rest of the field in their wake, the two riders banged elbows and knees at 160mph, with Roberts ahead by inches at the finishing line.

Sheene crashed spectacularly on a number of occasions. In 1975 he was lucky not to be killed when he crashed at 170mph at Daytona, breaking both femurs, his wrist, collarbone and several ribs. But his most appalling injuries were sustained at Silverstone in 1982, when his bike crashed into the wreckage of another machine during practice.

For a while it seemed that both his legs would have to be amputated. But a series of operations, which involved the insertion of nearly 30 screws and plates into his smashed legs, not only saved them, but restored him to racing. By 1983 he was competing again, but inevitably he was not the force he had been.

Two years later he finally retired from the sport. In 1987, plagued with the problems Britain’s cold winters inflicted on his injured legs, he decided to emigrate with his wife and young family to Australia. There he divided his time between his business interests and racing commentating. He also competed in such celebrity events as last July’s “legends” race during the British Grand Prix meet.

He married, in 1984, the model Stephanie McLean. She survives him, along with their son and daughter.

Barry Sheene, MBE, motorcycle racer, was born in London on September 11, 1950. He died of cancer at his home in Australia on March 10, 2003, aged 52.