Out now in shops, my Doctor Who: Survival of the Fittest, for which I was asked to give Sylvester McCoy an unrepentant Nazi for a travelling companion. Herewith my 150 words from the liner notes:

My grandmother was convinced she’d been had. After gassing the nest and plugging up the holes, the exterminator returned a few days later to check on it. When he unplugged the entrance, a bunch of wasps flew out and away. But he assured us that the nest was dead, and that the fugitives were merely the last hatchlings, from post-apocalyptic eggs.

The idea of insect civilisation brings questions of its own. How would it operate? How would they feel about being born, already forced into incontrovertible specialisms? As her first act after hatching, a newborn bee queen will murder her twin sister in the neighbouring cocoon. Every insect must know its place. When Big Finish asked me to think on the implications of taking Klein’s ideology to logical conclusions, I drew on my childhood memories, and the concept of a group of creatures, born alone in the dark in the ruins of their world, then freed to fly away to an unknown fate. Where did they think they were going? Were they only following orders?

But there’s more; there always is. As with most scripts, there was a long process of pitching and repitching before everybody was happy with the ideas on the table. “Survival of the Fittest” was in my mind because at the time I was writing a book about Charles Darwin, and I was fascinated at the time with the pull exerted on early Darwinists by the eugenics movement, which, of course, fed into Nazism. I initially wanted to write something about the First Emperor of China, who really took fascism to its logical conclusion. He was raised by what was known in those days as Legalists, people who would do anything to get into power and anything to stay there. The legal system of his Qin dynasty included punitive maiming and institutionalised bribery, while many lower classes were reduced to super-specialised slaves, door-openers and power sources. Hence my original pitch, which was called The Hidden Offices, taking its name from the title of the First Emperor’s personnel division for disabled slaves.

But Big Finish wanted something interstellar and far-ranging, so instead I pitched the concept of a world high above the galactic plane, where the Milky Way itself spun “like a swastika in the sky.” My working title, in fact, was Swastika Night. There was some stuff in there about warp cores and gravity wells, too, and a malfunctioning drive that had marooned human colonists millions of light years away from a solar system large enough to truly support them, forced instead to struggle for lebensraum with indigenous insectoids.

I wanted insects because of the parallels between hive societies and a fascist regimes. But once I had insects, I was drawn inevitably to a recurring issue in my Doctor Who scripts: how does the TARDIS translation circuit actually work? If everything somebody says is translated fully, why do we hear accents? Are accents part of semantics, in which case should we hear stress in unstressed languages? What size of area does TARDIS translation affect? What happens when it’s gone? And in this case, what happens when communication is conducted by pheromones and scents? When creatures have no vocal chords, how would the TARDIS render their communication?

When I realised that there would be little scope for humour, sarcasm or untruths in a pheromone-based communication system, I had my story. And then it was down to producer David Richardson and director John Ainsworth to make all the actors play creatures that communicated by smell. Everybody likes a challenge.