Eat.

Peter Ackroyd on his written procession of mystics and evangelists, heretics and headbangers ...

On the wall beside his desk are portraits of some of his other subjects: John Milton, Oscar Wilde (in whose voice he wrote a novel), the Elizabethan occultist John Dee. “You develop an affinity and eventually a sort of companionship, when you get to know them well enough,” he says. “Of course, that’s an illusion. But it’s something which spurs you forward.”

He says there is a fleeting quality to these friendly obsessions that puzzles him, though he doesn’t interrogate it too closely. “Most writers, I presume,” he says, “keep a sort of a memory of events and details of people’s lives when they write a biography. But in my case, it just completely vanishes once the book is done.”

He wouldn’t be much use in a pub quiz?

“It would be embarrassing. The things I wouldn’t be able to remember about Dickens, say [subject of a 1,000-page plus Ackroyd bestseller]. I can now hardly remember who he was married to or the names of any of his children or the order the books came in.”

He likens his methods to “a form of intellectual bulimia: you eat a great deal of knowledge. And you sick it up. And then you start again.”