Mandelson: The Real PM? London Film Festival

It is fitting that Hannah Rothschild's documentary about the Labour politician Peter Mandelson should appear just as Hammer Films is about to release its first movie in many years. After all, Mandelson's nickname is "the Prince of Darkness".

Rothschild's film was shot in the build-up to this year's May election. Its approach is akin to that of the cinema verité practitioners in early 1960s America who filmed Senator John F Kennedy from dawn till dusk in Primary (1960) and broke new ground in showing politicians in off-duty moments. The irony is that with Mandelson, there are no off-duty moments. He may kick his shoes off now and again, or stand impatiently by while his dog lifts its leg, or spend a few hours watching A Single Man, but it is clear that what his mother used to call "beastly politics" dominates his every waking minute.

The film-maker shoots Mandelson in the back of his ministerial car, on trains, and in what appears to be his home. He allows her to ask anything she likes. But Mandelson, even in ostensibly private moments, is very careful in what he says. "Peter has the best command of language," press officer Peter Power notes, and what he means is that he is circumspect in all that he says. If Mandelson does have what he calls "a hinterland" beyond politics, he is not keen for Rothschild to go there.

We learn of his continuing admiration for Tony Blair, his grave suspicions about Alastair Campbell and Charlie Whelan, his steeliness, and the streak of masochism that draws him again and again to the frontline of politics. He was happy to be a "lightning conductor" for Blair, and jokes that he is still up for being anybody's "scapegoat" if that is the role required of him.

Just occasionally, Mandelson betrays flickers of emotion but he remains the same stubbornly inscrutable presence at the end of the film as he is at the beginning. You can't help but admire his self-discipline and his work ethic. Whether he is changing his trousers and fussing with his cufflinks in his office before a Mansion House speech or eating a sandwich, his demeanour never changes. You could imagine him being played by Peter Sellers in a Being There-style comedy. His impassivity makes him all the more fascinating.

As a character study, Mandelson is not very revealing, but it does provide an engrossing look at the run-up to the general election. The shadow Foreign Secretary, William Hague, is shown in Parliament, describing Lord Mandelson as "the most powerful unelected deputy since Henry VII appointed Cardinal Wolsey, except that Cardinal Wolsey was more sensitive in his handling of colleagues than the noble lord". Hague was only partially right. Mandelson never has achieved real power. As he points out, he entered Parliament in the early 1990s; Blair and Brown had a decade's start on him. He may have been a key architect of New Labour, but his fate was always to be behind the throne, and never on it.

'Mandelson: The Real PM?' screens at the London Film Festival on 24 & 27 October