Rush - the new Ron Howard film about James Hunt and Niki Lauda - blurs the lines between fact and fiction All of this is conveyed in visceral detail: here at last is a movie that actually comes somewhere near to explaining why people are obsessed with cars whizzing around a track - and particularly with the races of that period, with old-fashioned gears and steering requiring levels of endurance hard to imagine now. The motivating force of the movie, however, is the rivalry between Hunt and Lauda, between the glamorous English playboy with no sense of risk and the austere, brilliant Austrian who calculated the odds. Peter Morgan, writer of The Queen and Frost/Nixon - which Howard also directed - wrote the script after many meetings with Lauda. He was impressed and fascinated by him yet at the same time, as a teenage boy growing up in England: "I loved James Hunt. He was so sexy, anarchic and beautiful. So the movie is a tribute to both men, to their on-track battles and off-track respect. But although Lauda has been closely involved with its making, he has allowed his character to be portrayed in ways that are not entirely truthful. For example, after Hunt's victory in the Spanish Grand Prix - the first sign that he might actually challenge Lauda for the title - it is Lauda who reports the McLaren car for being an illegal width and gets him disqualified. It was not; it was a member of the Ferrari team. Equally, when Lauda calls a drivers" meeting to try to get the fateful German race cancelled, on screen it is Hunt who leads the opposition, giving the impression that Lauda is attempting to rig the championship. It is never mentioned that the rivals were friendly enough to share a flat as young men; there is a famous photograph of them chatting that reveals levels of kinship that the film only belatedly hints at. It makes for a great story, as told on screen, but it is not absolutely accurate. Morgan says he was very conscious of the responsibility of this. "At the end of the film, I don't think you leave the cinema in any doubt whatsoever about the affection and respect between the two men," he told me. "I nudged it by no more than 10 per cent but if I over-egged the drivers" meeting, for example, I under-egged a lot of other things, such as James's sexual behaviour and his use of narcotics and alcohol. My conscience is completely clear. In fact, Morgan has readdressed the balance in some instances. It is true that when Lauda returned to racing, his face terribly scarred, a photographer made a joke about his wife not wanting to look at him. It is not true that Hunt beat the photographer up. This mixing of fact and fiction is inevitable in films such as this. As Ron Howard said: "It is not a documentary, it is interpretative." But it does matter. By chance, we meet at the weekend that Sir David Frost has died, and every single appreciation makes great play of his interview with President Nixon. Yet, as Morgan reminds me, that interview only achieved its current level of fame when he used it as the basis for Frost/Nixon. "When I started researching those interviews were not in any part of the Watergate canon," he said. And I am both delighted to have brought them to people's attention and also feel very responsible for the fact that I am writing this kind of stuff. Howard concluded our meeting with an anecdote about a man who utterly hated his film Apollo 13, also based on a true story, about the battle to save the three astronauts on the doomed space shuttle. It's the ending. It is so Hollywood. Those guys would never have survived," he replied. Which all goes to show that the relationship between truth and fiction is never simple. Rush is released on Sept 14