“You know the book is written in the first person, a very narrow first-person point of view, which is a hard thing to adapt.
“And it does other things, which are very difficult to put on screen, obviously, the travel but also then skipping around in time, there are 180 chapters, and it’s very fluid within a novel.”
However, the author later opened up about enjoying the process and challenge of this.
He added: “It was always going to be a challenge. At the same time, I wanted it to have a kind of that sumptuous, sunny, bittersweet quality as well.
“So it wasn’t that my intention when I wrote the book, but I loved the challenge of doing it.”
Us is airing on BBC One on Sundays and is available to stream in full now on BBC iPlayer.