“It’s always weird talking about sex in my books in England because I feel like there’s a particularly harsh measure of what’s OK to write about and what’s not,” he said.

His bestseller, Freedom, was nominated for the Literary Review’s Bad Sex in Fiction Award in 2010, a decision that still rankles.

“The Bad Sex Award is an English award, right?” he asked. “What was wrong with what I wrote? I don’t get it.”

At the time, the Literary Review noted Franzen’s “propensity for innuendo which comes over a bit Benny Hill”.

The passage which caught their attention included Franzen referring to “a protruding pencil of tenderness”.

His interviewer at the Cheltenham Literature Festival, the writer Clare Clark, did not provide much consolation when she told him that being nominated for the Bad Sex Award was “a twisted English compliment…they only award it to people who are good enough writers to know better.”

Franzen said Clark had not offered him “a pathway to feeling ok about it”.

‘Our vocabulary is so impoverished, and you either end up being pornographic or sugary sweet’

Defending his sex scenes, he said: “Sex is a big part of people’s lives, particularly young people. I can’t just draw a curtain over it because how a particular moment of sex plays out is important.

“I know for myself that I have memories of those moments and they’ve stayed with me because they were sometimes great, sometimes terrible, sometimes super-awkward, sometimes remarkably not awkward.

“In every case, I remember it vividly and I wouldn’t want to simply close off that part of what a person experiences or remembers because it might make someone uncomfortable to read about it.”

Also at the festival, Sebastian Faulks discussed the awkwardness of sex, which he said was “traditionally thought to be impossible because our vocabulary is so impoverished, and you either end up being pornographic or sugary sweet.

“The fact it’s so difficult doesn’t mean you shouldn’t try, although of course, in the back of your mind, there’s always the Literary Review’s Bad Sex prize.

“One of the things I learned, thinking about this years ago, was that there’s no point in describing two people making love because everyone knows what happens. The only reason to go into any detail at all is if something is disclosed between the two people.”

Franzen, during an interview conducted via videolink from the US, also discussed the thorny topic of white privilege.

“In fairness, I’m a privileged white male writer and it is past time to be questioning in a serious way, collectively, what that privilege means.

“It doesn’t feel that way to me personally because I just grew up leading my life, but I have reached a position of visibility that makes me able to understand why people would look at me as a symbol of that kind of privilege,” he said.

When writing non-white characters, white authors should ask themselves if they were doing it with appropriate sensitivity, Franzen said, but he added a warning.

“I do think for white Americans it is incumbent on us to be careful, and to really look hard and think hard about what we are doing when we render non-white characters.

“But obviously you can’t restrict writers to only writing about characters close to themselves, because it’s a recipe for the death of fiction,” he said.