The shocking truth about one of the cinema's best loved stars was exposed yesterday, a secret concealed for decades beneath a veneer of magic.

One man knows the truth, having spent years as one of the star's most devoted companions, and yesterday he revealed all.

The phantasmagorical fact about Chitty Chitty Bang Bang is that under that glittering mask of teak, brass, leather and chrome, the beating heart is ... a Vauxhall Ventura engine.

"Runs like a dream though," said Philip Watson, the mechanic who guards the car like the crown jewels at a centrally heated private store in Norfolk. "Needed a bit of work when she first came to us, but no trouble since."

The car caused a spectacular traffic jam yesterday, as a rubbish lorry tried to squeeze past in the narrow street outside the London Palladium. It was there to publicise the first stage version of Chitty Chitty, a £6.2m show which will open next April. Big musicals, heavily dependent on tourist audiences, have been the worst hit in the theatrical gloom since September 11.

However, Barbara Broccoli - co-producer and daughter of James Bond producer Cubby - yesterday expressed unwavering faith in the flying car. "It's part of everybody's childhood and everybody loves it." It was very much part of her childhood: the infant Broccoli may be spotted in a fairground scene in the film, which her father produced.

The film was based on a children's book by Ian Fleming, about Caractacus Potts, an eccentric inventor who converts an ancient racing car into a flying and floating machine.

The musical will have 18-year-old newcomer Emma Williams as the heroine, Truly Scrumptious, with a cast of veterans, including Michael Ball, Richard O'Brien, and Brian Blessed.

Show business has resolutely ignored the motoring legend that the name, derived from that of a real car, was based not on a backfiring exhaust, but on a bawdy first world war song about soldiers obtaining a pass - or chitty - for a weekend's R&R.