But Fielding said that Johnson — who has been criticized for stoking Islamophobia, including through his book “The Dream of Rome,” which included an appendix saying there was “more than a grain of truth” to the idea that the “real problem with the Islamic world is Islam” — was trying to show he was a liberal Conservative to appeal to voters in the early 2000s. Johnson would write a different novel today, Fielding said.

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“Johnson’s a political chameleon,” Purnell said. “He was left-leaning London’s mayor and now he’s going for the far-right Brexit crowd. He was once pro-immigration, and now we’re not so sure. He was a petrol head and now he’s made himself an eco-warrior. There are no core beliefs, no values, just instincts.”

Gimson agreed that the book showed Johnson’s lack of core beliefs but said that was a good thing for a potential prime minister. “Both in politics and the arts, you shouldn’t be improbably reaching after certainty,” Gimson said. “Politicians often get stuck with an ideology that makes sense at one point, but circumstances change.”

The book’s sympathetic portrayal of a terrorist showed Johnson’s humanity, Gimson added. “People often miss that about him,” he said. “There are strong feelings hidden behind all the jokes.”

In 2005, Johnson talked about “Seventy-Two Virgins” on “Desert Island Discs,” a British radio show where celebrities are asked about their favorite music (Johnson picked Brahms, Beethoven and “Pressure Drop,” by the Clash).

Sue Lawley, the show’s presenter, called the book “chillingly prescient.” But she then asked Johnson why he’d written a novel that reminded people of his own extramarital activity. “You do like playing with fire, don’t you?” she said.

“I suppose there might be an element of truth in that,” Johnson eventually replied .

Johnson has not left writing behind. He is working on a book about Shakespeare called “The Riddle of Genius,” due in 2020. In June, Johnson said that deadline would slip if he became prime minister.