A profile from the Independent

Peter, 55, confirms to me that he was implying in his review that Christopher, 58, was closer to religious belief than he had ever accepted. " There is always, in the atheistical struggle with God, the fight against temptation. If it didn’t matter to you, why write a book about how wrong it is? The first person you have to convince with any book you write, is yourself. If you didn’t need convincing… why go to all those lengths?"

On a book tour in Los Angeles, Christopher agrees to read the review by email and then flatly rejects the idea that he is, as he put it, a " repressed seeker". Prefacing his response to his brother’s review with faint praise – "a quite stirring and eloquent piece" – Christopher says: "The sickly idea that this interest is a disguised cry for help… only demonstrates the insecurity and the bad faith of the godly." The elder brother then adds: "Though I slightly dislike to say this, [Peter] offers himself as yet another example of how the religious mentality forces honest and reasonable people to say dishonest and irrational things."

This exchange is merely the most recent of a long line of clashes between two brothers who make up a unique phenomenon in the world of journalism. Normally, they tend to pass each other by, partly because they operate on different sides of the Atlantic, with Christopher based in Washington. " Quite a lot of people who read Christopher don’t know that I exist; and quite a lot of people who read me don’t know he exists," Peter says. " We live in different worlds."

Once, however, they were something close to brothers in arms. They grew up in boarding schools around England and Scotland, constantly on the move thanks to their father’s postings as an officer in the Navy. In their early teens Christopher led Peter into an interest in radical politics, and both spent their university years (Christopher at Oxford, Peter at York) fighting for the International Socialists, something of a minority within a minority: a Trotskyist faction.