Speaking exclusively to RadioTimes.com about the tonal shift of it all, Brooker said: "It might sound odd, but it came from two separate ideas that then glommed together.

"There was one I wanted to do - a kind of horror story about somebody restoring old horror movie footage who then realises they can communicate with people in the footage.

"That was an idea I'd had, and I couldn't quite work out what the story was. And then I also wanted to do a story about an actor, like someone who's sort of unsuitable, who gets thrown into the role of James Bond in a high-tech remake of an old Bond movie.

"These were two separate ideas I was toying with for quite a long time."

He continued: "And then I think what happened is I watched Brief Encounter, which I'd never seen before, and I thought, 'Oh, yes, a vintage romance – that would be fun.'

"And then those two ideas sort of went, blink, and then suddenly you got the ending.

"And so really, that was the germ for the whole thing. And then when you're sort of thinking the story through, it kind of leads you into places. I was like, 'Oh, it's a romance.'

"I like it every so often. It’s nice to write a romantic episode now and then. It's, like, a bit soppy."

Executive producer Jessica Rhoades also added: "It’s the most Charlie thing that it started as a horror."