Politics is said to be showbiz for ugly people, but a sexual thriller is to portray “Tony Blair” and his Downing Street circle in a flattering light.

In the cinema adaptation of Robert Harris’s novel, The Ghost, the former prime minister – or a character suspiciously similar – will be played by Pierce Brosnan, star of four James Bond films.

The director will be the Oscar-winning Roman Polanski, while “Cherie” is to be played by Olivia Williams, who starred alongside Bruce Willis in The Sixth Sense.

In a touch that may dismay the Blairs, however, the love interest is Kim Cattrall, the Sex and the City actress, who will give a vampish portrayal of a character not far off Anji Hunter, the former prime minister’s confidante and Downing Street “gatekeeper”.

Hunter’s alter ego in the novel has a far closer relationship, as she and the premier are entangled in an affair.

When The Ghost was published last year, it caused a furore and Harris repeatedly refused to confirm it was even based on the Blair circle. It was hard not to see the similarities, however, between Blair and Adam Lang, the book’s ex-premier, who is looking for a ghostwriter, played by Ewan McGregor, for his memoirs.

The overbearing Ruth, Lang’s wife, has strong echoes of Cherie, while Amelia Bly fills the role of Hunter. Harris now admits that the characters were drawn from Blair’s circle.

The film’s cast are more attractive than the real personalities are perceived to be, however.

“We didn’t want lookalikes, but we did want and we’ve now got very attractive and very good actors for the key roles,” said Harris, who has also written the script of the film, which begins shooting in February.

Polanski, whose Oscar-winning films include Chinatown and The Pianist, will be directing in studios in Berlin and on the island of Sylt, off northern Germany. The island will double as Martha’s Vineyard, the American establishment’s resort off the Massachusetts coast where much of the book is set.

The roster of names such as Polanski, Brosnan, Cattrall and McGregor shows Harris has stepped up a rung on the cinema ladder. His novel Fatherland was turned into a made-for-television film, while Enigma, another adaptation, starring Kate Winslet, Matthew Macfadyen and Dougray Scott, was moderately successful at the cinema.

Harris and Polanski, who lives in Paris, have been closeted together for the past four days in the French capital working on the final script. “It follows my book very closely,” said Harris.

The plot’s storyline delves into the murky pasts of the Langs and their close ties to America and ends with a twist.

It also depicts affairs between Adam Lang and Bly, and another between Ruth Lang and the Ghost.

In the past, it has been hinted, without evidence, that Blair had a fling with Hunter before he met Cherie. In the book and the film, Ruth Lang is clearly jealous of Bly.

“This is a psychological and sexual thriller,” said Harris. “It’s a four-person sexual drama. But it was not a bonkbuster book, and nor will it be a bonkbuster film.”

Brosnan was Polanski’s first choice to play Lang as he wanted a charismatic figure as the former premier. Williams, 40, also starred in this year’s BBC drama Miss Austen Regrets.

But perhaps the biggest surprise is the casting of Cattrall, who was born in Britain and only found fame in her forties as Samantha Jones in Sex and the City.

The film should be completed by next autumn with its release soon after. “I want to be sure it’s out before Tony Blair’s own memoirs are published,” said Harris.

In October 2007, four months after he left office, Blair finalised a £4.6m deal with Random House, the publisher, for his memoirs. The firm will not say how much has been written or give a date for publication.

Will Blair, like Adam Lang, have someone else to do the writing? “There will absolutely not be a ghost,” said a senior executive at Random House. “He is writing himself.”

Screen PMs

Prime ministerial portrayals – what the critics said:

“A Cheshire cat-grinning schoolboy, bursting with coltish enthusiasm.” Michael Sheen as Tony Blair in The Queen, 2006

“My first reaction is, ‘Nah, that’s never Maggie, looks nothing like her’. That and ‘phwoar’.” Andrea Riseborough in the BBC’s The Long Road to Finchley, 2008

“His stuffy drawl through his soup-strainer moustache is spot on.” Jeremy Irons on stage as Macmillan in Never So Good, 2008

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