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Only one of the real-life antagonists in Frost/Nixon can be present when the film receives its world premiere in Leicester Square tonight.

Richard Nixon died 14 years ago, but the interviewer who persuaded him to apologise for Watergate is very much alive and looking forward to seeing his finest hour commemorated in the opening film of The Times BFI London Film Festival.

However, Sir David Frost’s evident delight at becoming a bona fide Hollywood hero is very slightly tempered by the liberties that the hit play, and now the film, have taken with his own achievements. For most of the two-hour running time “Frost” is depicted as a frivolous lightweight and, although the real Frost understands that this accentuates the drama, it rankles that posterity will inherit a warped idea of his career before the Nixon interviews.

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“It’s an interesting situation to be in,” he said yesterday, with a nervous laugh. “It’s not my film. [He gave up editorial control but retains financial rights.] It’s just . . . my life!

“There’s 10 or 12 per cent of fiction in there, one or two bits of which I could do without.”

Frost, 69, has seen the film twice and thinks that it is “brilliant”. However, he regrets that “to build up the underdog thing”, Peter Morgan’s script downplays what was already a distinguished television career before the interviews.

Frost/Nixon is set in the summer of 1977, when more than 45 million Americans, a record for a news programme, watched transfixed as Frost, a Briton best known to them as a chat-show host, wrung a stunning confession from their disgraced former President.

Nixon admitted for the first time the extent of his guilt over the Watergate scandal, saying: “I let down my friends, I let down the country, I let down our system of government and the dreams of all those young people that ought to get into government . . . I let the American people down. And I’ll have to carry that burden the rest of my life.”

The award-winning play, which Morgan describes as “a thinking person’s Rocky”, opened at the Donmar in 2006 before transferring to the West End and Broadway. The drama is now poised to reach a much wider audience, many of whom will never have heard of Through the Keyhole or Frost over the World, the interviewer’s weekly programme for al-Jazeera English, let alone The Frost Report and That Was the Week that Was, the taboo-shattering satire that launched his career.

The production notes describe Frost as “a jet-setting featherweight television personality with a name to make”, and the early part of the film depicts him as a shallow playboy whose career has hit the buffers.

In the film, while Nixon’s team consider Frost’s surprising $600,000 offer for the interviews, the presenter is filming a low-budget item with an escapologist in Australia.

In Frost’s mind, it wasn’t quite like that. “That’s one of the things that I’m not mad about,” he said, carefully.

Frost does not accept that his career was in decline in 1977, much less that he was primarily the light entertainer that the film suggests. “In fact, by that time I’d interviewed two or three presidents, two or three prime ministers, Moshe Dayan [the late Israeli Defence Minister], the Archbishop of Canterbury, a whole list of people. I had done a hell of a lot by then.

“A lot of people thought that one of the reasons Nixon said yes was that he wasn’t aware of a lot of the more serious stuff that I had done here [on British television].”

Morgan spoke at length to many of the people involved in the original interviews, including Frost, and he has always defended his blurring of fact and fiction because “everyone I spoke to told the story their way”.

Frost is, mostly, delighted with the results. He agreed that “among the fictions is one of the most brilliant parts of the film” – an entirely imagined late-night phone call from Nixon to the Frost character that unlocks the interviewee’s damaged soul and proves to be the key to the next day’s scoop.

Frost also praised the “great job” that Ron Howard, the director, had done adapting the play for the screen, and heaped plaudits on Michael Sheen, who plays him, and Frank Langella, who “has caught the soul of Nixon”.

Frost/Nixon is set to be one of the critical successes of the year and is tipped widely to be one of the front-runners when the Oscar nominations are announced in January.

The festival runs from today until October 30.

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