I’ve heard executives ask what the point is of having a gay relationship when it’s off-putting to so many people. You’ve said: “It had to be for TV because, with a gay relationship at the centre of the story, it would have been impossible to fund a movie.” They disappear into the roles and you can’t see any of the work that goes into it. I loved Wolf Hall – Mark Rylance and Ben have the same magic. We’d love to say something was categorically a lie. We all kind of know which lies we were told, whether it’s about wars or government policy, but without the evidence, you can’t pin someone down. Accumulate data on how they spoke, then use this algorithm to test any statement they’d made. I took it to the extreme, running it without people’s consent. If I’d moved into something topical like real-world terrorism, what would that have had to do with their relationship? That would have no resonance beyond being the thing that killed his lover. It was whether their love story was real: did Alex really love Danny? That was the key revelation. The big question wasn’t who killed Alex or anything about the spy world. When I wrote it, it didn’t cross my mind that he’d be alive. So you never intended Alex’s fate to be ambiguous? There wasn’t much I could do about that, but I was pleased because it meant the relationship worked. A lot of people tweeted me, really sincerely pleading for Alex to be alive. Danny and Alex were lost in very different ways, then found each other.

Lots of people out there are struggling to find their way. Why have people responded to London Spy on such an emotional level?

London spy tom rob smith