The old eat the young. That is the back-of-a-beermat pitch for new Channel 4 drama Generation Z. And because the Z stands for zombie, the eating is meant literally. “I loved the idea of a horror story about societal breakdown, told from the perspective of different generations,” says its writer-director Ben Wheatley. “Once I started writing it, I couldn’t stop.”

The film-maker’s first original series for TV begins with an army convoy crashing outside a care home. The subsequent chemical leak turns the residents into marauding monsters who attack local youngsters. “It’s a bit of a Brexit metaphor,” admits Wheatley. “But it’s by no means binary. We discuss it from each generation’s viewpoint, exploring the notion that boomers have ruined the lives of the young. Because it’s a genre piece, that’s basically by biting their hands and eating their brains.”

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“I love telly and watch a lot of it – Battlestar Galactica, The Sopranos and Deadwood were the golden age for me – so I was keen to play with a different train set,” he says. “It was exciting to write in longer form, rather than the sprint that is a film script. In terms of production values and cinematic scale, TV has closed the gap on film. It’s like the difference between a single and an album. Actors move freely between the two now. The skillset’s no different. Any stigma has long gone.”

Fittingly for a series punctuated by gruesome deaths, he’s assembled a killer cast. Playing the pensioners are veterans such as Sue Johnston and Anita Dobson. “Sue’s first day on set, she was biting someone’s nose off,” he says. “They got to do stuff they don’t usually do, running around covered in gore, and had a blast doing it.” The gore is created the old-fashioned way. “Everything is practical, with prosthetics or models. There are very few CG effects. When arms are ripped off and blood spurts, there are people pumping plasma just out of shot. We use jelly when organs need to be edible. It’s all very visceral.”

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Generation Z is coming to Channel 4 this autumn.