Their affair is discovered by the tabloids and the party spin doctors

Their affair is discovered by the tabloids, and the party spin doctors move in. Cartwright, who was a spin doctor before turning novelist, knows whereof he writes.
We meet to talk about the novel, Half in Love (Sceptre, £16.99), on a dark grey London morning at the Groucho club in Soho, itself once a celebrity among clubs. The woman on reception has a no-nonsense routine with the C-list regulars who still keep the place buzzing; she calls them love, and you can see she’s one to treat all celebrities the same. In a peculiarly English way, this makes them feel more grounded than any amount of fawning.Cartwright is recognised here as soon as he walks in, and given a “one of us” hello as he strips out of his cycling gear. He is instantly identifiable as a type of male writer who thrives in London.

Living in the capital – most of the time – though not necessarily born in Britain, these men are in their fifties but fit from playing tennis. They make their living writing literary but readable novels, quite regularly optioned for film scripts. The leader of the pack is Martin Amis, of course, but it includes others like Julian Barnes and William Boyd.They admire older American men like Saul Bellow, Philip Roth or John Updike, and will cite them as influences. However, Amis excluded, the literary celebrity they find here is a far paler thing than that which cloaks the Americans.Cartwright, born in South Africa and the son of the editor of the Rand Daily Mail, has lived in England since studying at Oxford. He is at that interesting moment in his career when his fame is growing – though he comes late to it by the standards of the other men.In the new novel, the affair is first outed by a journalist interviewing the actress in an anonymous hotel room, as I am interviewing Cartwright. Having shifted professions several times, he is edgily aware of both the writing and the being written about.

Cartwright started his working life in advertising, where he won plaudits for “Believe it or not, Prime Pal is for dogs”.He switched from advertising, and wrote two detective stories because he thought that they would be commercial. Dissatisfied with commerce, though, he set out to find his true writing voice.In the late Seventies, he also became a prototype spin doctor before we knew the job, let alone the job description. He managed election broadcasts for the Liberal Party, and then the SDP Alliance, during the 1979, 1983 and 1987 elections.Cartwright repeats the received line on David Owen – about what a nightmare he was to work for – but also says that he believes that most politicians are misrepresented “I know the sort of pressures these people are under. The popular image of them as a bunch of self-seeking, useless people just isn’t true.”I think there are inherent character flaws in them,” he says. “You wouldn’t take the job unless you were a megalomaniac of some sort.

But my experience of the two or three with whom I worked closely was how hard they worked, and all the time under this fierce, appalling scrutiny.”In the middle of a campaign on which Cartwright worked, David Steel was falsely accused of having an affair “The pressure was indescribable. Imagine, in the middle of an election campaign, having to go talk to your wife and say, you know, you’re about to hear… it’s incredibly tough.”In those days, he had to learn to manage the media Steel and Owen used to travel in separate coaches. The papers would send one journalist in each coach to ask identical questions, and then highlight the differences in the replies Cartwright put a stop to that.

“As you know,” he says, “you can take an interview and take the bits out of it that suit your thesis, without being inaccurate You’re probably going to do just that to me. You’ll go away and write: ‘novelist sitting in posh Groucho club; obviously spends far too much time there’. I don’t drink, by the way,” he adds, as if dictating.But while the material for the book is grounded in his experience, it is not factual. The PM’s wife in the story, though she answers the door dressed for court, is not the real Cherie Blair.