However, when he wanted to write a book imagining what would have happened had Hitler won the second world war, he hit a barrier.
“The tools of non-fiction were insufficient to allow me to express what I wanted to say; it could only be done imaginatively,” he tells me over coffee in Dublin.
“Once I started tackling a subject with imagination rather than straight on, I never looked back. I have never, since, written non-fiction, and I don’t think I ever will.”
Fatherland, published in 1992, was an overwhelming success, and the 10 novels Harris has written since have built his reputation further. I suggest he has an innate sense of the zeitgeist.
“I don’t feel that consciously but I have always been interested in politics and the world around me. I’m constantly trying to find a way to assemble all this into a narrative that satisfies me,” he says.
“I don’t think I could write about a serial killer; my heart would not be in it. I am trying to make sense of my world, and there always has to be some sort of political edge to it. It’s possible to range over all kinds of periods and countries, because you can see the same pattern there as well,” he says.
His new novel, Conclave, is set a few years in the future. The Pope is dead, and behind locked doors, 118 cardinals get ready to cast their votes. Harris has already covered ancient Rome in his Cicero trilogy; Imperium, Lustrum and Dictator, but what drew him to this ancient Catholic ritual?
“You have 120 men locked up for several days trying to work out who should be Pope; there must be something going on, it can’t all be prayer; there had to be some sharing of thought, and politicking, and it’s clear that there is,” he says.
Harris always conducts a great deal of research before he starts writing, and for Conclave he was granted help from the Vatican. They gave him a tour of all the relevant locations, from the Sacristy of the Sistine Chapel, the Pauline Chapel, and the room of tears where the new Pope is robed.
He was also shown Casa Santa Marta, the surprisingly spartan building where the cardinals stay during a conclave.
He gleaned essential information from a cardinal who has attended a conclave, but it was the existence of a secret diary that enabled him to write the book.
“A diary of the 2005 conclave was published in an Italian magazine, and it’s never seriously been challenged.
“It stated that when the liberals realised that Cardinal Martini didn’t have numerical strength, in an attempt to stop Ratzinger, they switched votes and gathered around our present Pope. He got the required third of the vote, and that delayed Ratzinger’s election. The moment I read that I had my characters.”
In Conclave, Tedesco, Archbishop of Venice is the top contender; fellow Italian Bellini is favoured by the liberals; the Canadian Tremblay, clever at playing the media seems set to gather momentum, and it’s possible that the traditionalist Adeyemi may make history and become the first black Pope.
The thriller proceeds at a cracking pace, with many twists and real suspense, but it’s the sense of authenticity around the conclave; the nuggets of real history, and the stultifying atmosphere which is ripe with intrigue that make this such an impressive read.
An unbeliever, Harris dislikes atheism. “It’s boring and obvious. The easy sneer of the atheist repels me rather, even though I can’t claim to have any kind of religious faith.” He pauses. “But I would like to.”
Indeed, it is clear, from his writing, that while disliking many Catholic practises, and especially its attitude towards women, he has a great deal of empathy for the cardinals he writes about.
And especially Cardinal Lomeli, who, as Dean of the College of Cardinals presides over the election. We hear the story from his point of view.
During the grand mass, abandoning his prepared homily, Lomeli improvises, feeling the distinct presence of the holy spirit. This passage was utterly convincing. As a non-Catholic, wasn’t that hard to achieve? Harris points out that he’s written as a Roman water engineer, and a 19th century French officer.
“It’s the job of a novelist to get into the heads of characters and to make them plausible, and there was enough in Lomeli to empathise with. He is facing doubts in his faith, yet he keeps the show on the road.”
Harris’s writing journey started when he was six, and wrote an essay titled, ‘Why Me and My Dad Don’t Like Sir Alec Douglas-Home.’ He progressed to plays, put on by his classmates, and at Cambridge was president of the Union and editor of the student newspaper. His BBC gigs included both Panorama and Newsnight.
Once close to Tony Blair, Harris is now disenchanted with politics.
Contrary to public belief, he says that The Ghost is not about Tony Blair per se, and that writing it was not meant as an act of revenge, but he’s had no direct contact with Blair since the book’s publication, in 2007.
“It was just such an interesting subject,” he says. “You find a character, you find a situation, you think up a story and see how the whole thing works.
“I had the idea of writing about a ghost writer some years earlier, before I had met Blair, and then the right time came.” Post Brexit, having voted Remain, Harris is in despair.
“It’s like Munich was and Suez. It has split families. This is fundamental into our future and the future of our children, and it is hard not to be emotional. It’s caused a major rupture in the way the UK is progressing.
“There are certain people my wife (writer and columnist Jill Hornby,) will not sit beside, or have in the house, of if they come, will not serve dessert to.” Would he ever enter politics, to help put things right?
“No. I wouldn’t. It wouldn’t suit my lifestyle, and I’m naturally contrary. The moment someone wants me to run in one direction, I run in the other. I’d be disloyal.”
A family man, with four children aged 16 to 26 — Harris lives in Kintbury, Berkshire, and has a house in the south of France. “The great joy of being a novelist is that I’ve been in my children’s lives all the way through. We have a good relationship.”
His ambition is to continue to write. And, although he has won prizes — An Officer and a Spy won four — it is sales and a wide readership that matters most to Harris.
Early reviews to Conclave have been mixed; some wildly enthusiastic, others, finding the ultimate twist unconvincing.
“I expected that,” he says. “Of course I would prefer solid praise, but I’m rather suspicious of books where that happens. I think if a book is any good it provokes strong reactions. I would trade all reviews for sales, and so far, in the UK, Conclave has been my most successful.”
I ask him what he plans next.
“I’ve come full circle,” he says. “The next one is set in Germany in the 1930s. I have earned the right to have another Nazi uniform in a novel having not done so for 25 years.”