In icy Berlin this weekend, there have been plenty of requests for interviews with Roman Polanski, whose new film The Ghost Writer premiered on Friday. Of course, although some of the more absent-minded media hadn't noticed it, Polanski is far away in Switzerland, under house arrest in Gstaad, still facing the consequences of that statutory rape charge more than 30 years ago. He wasn't in town for the film's packed press conference. In his absence, the film's stars and producers fielded respectful, generally softball questions, agreeing among themselves what a demanding but talented craftsman the Pole is while largely declining to discuss his private life.

The Ghost Writer isn't vintage Polanski but is still a strangely potent and disorienting film that works on many levels. The politics are foregrounded. It may be coincidence that the film is receiving its first screenings bang in the middle of the Chilcot inquiry in Britain and at a time when yet more damaging revelations about UK security services are emerging in the press. Nonetheless, the screenplay (which Polanski co-wrote with Robert Harris from Harris's novel) is full of elements that will seem instantly familiar.

There are very obvious parallels, too, between the story that The Ghost Writer tells and the current plight of the Polish director. The film is about an ageing celebrity in retreat, with the media pack in pursuit of him. The celebrity in this case isn't a film-maker suffering the effects of a sex scandal from long ago. It's a politician who has been accused of war crimes. Adam Lang (Pierce Brosnan) is an ex-British prime minister who, during his time in power, it is alleged, handed over suspected terrorists for torture by the CIA. The US is a safe haven for Lang: his American friends won't give him up to the war crimes court. The irony is apparent. For Polanski, the situation is quite the reverse. Europe provided him with sanctuary (at least until his arrest last September) while America was the place he most needed to avoid.

Lang is the ostensibly progressive politician who has cosied up to the right-wing US president. He is an ex-student actor who is able to smile for the cameras, even when accused of sending young British soldiers to their death.

In Berlin on Friday, the issue that preoccupied the press conference was less the Polanski sex scandal from the 1970s than the events leading up to the war in Iraq and ex-prime minister Tony Blair's part in them. Harris joked that the book he published as fiction in 2007 now seemed like documentary. The outspoken writer went on to rail against his erstwhile friend Blair and his part in the rush to war in Iraq.

"There is a lot of disquiet in Britain about that war. There was surprise that Tony Blair didn't make any gestures towards those who had lost people in the war," Harris commented. "People talk about the verdict of history in politicians as if it is going to come in 20, 50 or 100 years' time but the verdict of history generally comes now. I think there is a sense that we have the verdict on this war and its legality."

Polanski, though, isn't a British parliamentary reporter or political correspondent. You're never quite sure how seriously to take the politics in the film. At times, the indignation of the film-makers at the ruthless, cynical behaviour of the politicians seems evident.

However, The Ghost Writer is also a rip-roaring thriller with hints of John Buchan's The 39 Steps and Raymond Chandler's The Big Sleep about it. The film-makers don't seem sure whether they're preaching at us or trying to entertain us. The plot twists begin to multiply. Lang's ghostwriter's paranoia is likely to be shared by audiences as they try to work out which of the characters is to be trusted. Inevitably, the cheating extends to Lang's private life too.

What Polanski does capture very effectively, perhaps as a result of his own long experiences, is the fraught and complex relationship between the media and their prey. "The pack is on the move," we're told, as the news crews and journalists descend on the remote US island where Lang is living in a huge modernist house. We even feel a certain sympathy for him when the helicopter appears at his front window and the photographers' long lenses are trained on him.

Brosnan captures the strange mix of unctuous charm, defiance and vulnerability that characterises the ex-prime minister. As the ghostwriter, Ewan McGregor again affects the Dick Van Dyke-like cockney accent he used in Woody Allen's Cassandra's Dream but he gives a far more effective performance here. He is the cheeky, quick-witted outsider, trying to cope as he is drawn into an ever more baffling and threatening world. The film has barely started when he is mugged and robbed.

There are plentiful echoes of Polanski's own earlier films. As in his thrillers Frantic and Bitter Moon, there is a melodramatic quality – a desire to push beyond realist conventions. Certain sequences, notably the final one, are deliberately very stylised. There is the same queasy claustrophobia here that is found in a film like Cul de Sac. McGregor has some of that mix of arrogance and innocence that characterised Jake Gittes in Chinatown. The bleak, deadpan humour is recognisable too.

Now well into his 70s, Polanski doesn't have quite the energy to lift The Ghost Writer beyond the realm of the conventional conspiracy thriller. In its lesser moments, the film is stagey and old-fashioned. The in-jokes about the publishing world are heavy-handed. The plotting relies heavily on coincidence and on what Hitchcock used to call McGuffins: scraps of paper, photographs with telephone numbers written on the back.

The Ghost Writer was made in Europe, at Babelsberg Studios in Berlin and on location. Its recreation of the US never rings true. Even when the plotting creaks, though, we're aware of its director's inventiveness and intelligence.

Polanski supervised the final part of the editing of The Ghost Writer after his arrest. The media obsession with him since then shows little sign of abating. That is one reason why there is such curiosity about his new film. However, for the duration of the picture at least, audiences should be able to forget about the notoriety of its director. Whatever his travails, Polanski is still capable of turning out a well-crafted and intelligent thriller with bite and irony.

'The Ghost Writer' is released on 16 April