A truck overturns in a quiet town and scatters a load that would be the last you would want scattered anywhere. It is my favourite way to start a zombie movie – or, in this case, television series, written and directed by Ben Wheatley – and soon we are off to the gory races.

The twist after this traditional setup is that the first infected are old – specifically the residents of two care homes. Cecily (Sue Johnston) is patient zero for one, her companion Frank (Paul Bentall) for the other. Also, the infection makes them not sicker, but better. These are talking, thinking, planning-the-best-way-to-get-more-delicious-flesh zombies, moving as a gang through a nearby forest, preying on cyclists, walkers, dog owners and – pet lovers beware – dogs. I am pretty sure Bentall, despite his long and storied career, never envisaged adding to the skills section of his CV “Punching through a dog and wearing it as a gauntlet-club”.

The young folk – well, they are busy being young. Going clubbing, bemoaning unrequited love, having misguided sex, buying drugs from a retired chap called Morgan, played appropriately by Wolfie Smith, by whom, of course, I mean Robert Lindsay. He has a marijuana farm in a basement and also, for reasons to do with an activist past, a lair full of CCTV feeds and lab equipment. He is your go-to guy if your sleepy town suddenly becomes infested by flesh-eating zombies and your own nan is not above trying to take a chunk out of you before your unrequited lover “kills” her with a crossbow.

The young people comprise: Kelly (Buket Kömür), the escaper of the chomping nan (Anita Dobson, probably having the best time of anyone as Janine); Stef (Lewis Gribben), a crossbow-wielder and a follower of a toxic online influencer, despite his fundamental good-heartedness; Charlie (Jay Lycurgo), Kelly’s ex; Billy (Ava Hinds-Jones), Charlie’s sister, who is part of the unit deployed to the village when Westminster realises something has been spilled that ought not to have been; and Finn (Viola Prettejohn), who is bolshier and wittier than the rest and the only one who amounts to more than a cipher as the six episodes unfold.

So! We have the old eating the young and saying things like: “Why shouldn’t I eat! I’ve been treated very unfairly … Why shouldn’t I have what I want?” as the latter race around trying to find a cure and undo all the damage being caused. If zombie films are always a way of examining the world around us, what could Generation Z possibly be mapping? Why yes, it’s Brexit!

The infection effectively allows the oldies to turn back time, to feel their bodies come back under their control, to pursue what they want again and to hell with everyone else – even (or especially) their grandchildren. That is how selfish a noxious particle (or idea) can make you.

There are also echoes of Covid. The kids have to take their A-levels suddenly, even amid the outbreak; respirators don’t arrive in time to protect the soldiers as they investigate the blood-spattered retirement homes and try to save civilians; and quarantines are imposed.

There are too many subplots that don’t cohere and diffuse the tension. These include various conspiracy theories, including one about the boyfriend of Charlie’s mum botching an attempted entrance into the world of county lines drug smuggling, which takes up far more time than its payoff deserves.

The mid-series episodes feel baggy and the tonal inconsistencies are distracting: sometimes, we seem to approach the world of 1984’s nuclear-war drama Threads; other times, it is more Shaun of the Dead. Occasionally, we could be in the latest, most desperate spin-off of The Walking Dead. The teenagers’ parents hardly get a look in, which seems a shame when you have Johnny Vegas and T’Nia Miller raring to go.

But it begins and ends well and earns enough goodwill to carry you through the sluggish parts. You need time to recover from the dog thing, anyway. The satire and the message aren’t subtle (at one point, things literally become splenetic) and become even less so when Cecily and Janine start fracturing the leave – I mean zombie – contingent, arguing about whether they should get their way at all costs and almost turning the show into Generation Agitprop. But it’s fun. At least, more fun than Brexit.