Keep Calm and Merge On.

The single greatest threat facing what remains of humanity after civilisation has packed up and gone home. 

It isn't the radiation. It isn't the roving bands of feral dog-things. It's the fact that even after the total collapse of society, we British and by extension, everyone who's absorbed enough of our culture to know better still cannot bring ourselves to just talk to people we haven't been formally introduced to.

Picture it. The end of the world. Two gangs meet on a motorway somewhere near what used to be Luton, both wearing bin bags reinforced with gaffer tape, both armed with sharpened bits of Ikea furniture, and instead of doing the sensible thing  establishing who's got the tea bags! they immediately start having a scrap, because apparently the apocalypse did not, in fact, come with an instruction manual on manners, and old habits die harder than we do.

Enter our heroine, a gang leader called Denise, who did not survive nuclear winter by being a berk. Denise looks at forty malnourished people fighting twenty other malnourished people over what appears to be a single tin of custard, and thinks: "This is mad. What we want is a merger."

Denise wants to combine the gangs. Pool resources. One big miserable extended family, queuing politely for tinned custard like the Blitz never really ended, it just got worse and lasted longer.

The trouble is nobody wants to merge with anybody, because the one thing that survived Armageddon completely unscathed, along with cockroaches and Piers Morgan's opinions, is petty regional grievance. Denise's lot don't want the other gang joining up because their leader, Big Nigel, "supports the wrong football club" a club that, it should be said, no longer exists, along with football, and possibly Nigel's memory of what football was. The other gang won't merge either, because "Denise's crowd have always been funny about sharing the good biscuits," an allegation dating back, apparently, to a garden fete in 2029.

This is exactly the same energy as a residents' association meeting, except the stakes have shifted from "the bins weren't collected" to "we shall all perish," and you'd think impending death might sharpen the priorities a bit. It has not. We will die on a hill  often an actual hill, given the terrain  over who gets to be in charge of the kettle.

Denise tries everything. A joint scavenging trip, which collapses into a row about who spotted the tinned mackerel first. A trust-building exercise, which in a world containing that many sharpened fence posts is spectacularly ill-advised. She even sets up a committee, and I'd like you to absorb that: society has ended, the sky is the colour of a bruise, and we've still managed to convene a Subcommittee for Snacks, complete with an agenda nobody follows and a bloke called Trevor who insists on taking minutes.

What finally does the trick  and this is, I'm afraid, entirely on brand for us as a species  is that Denise stops trying to make everyone get along and instead finds a third gang to unite against: one rumoured to have a working generator and, worse, "ideas above their station." Suddenly Big Nigel and Denise's mob are the best of pals, bonded by that most ancient and reliable of British adhesives: mutual disapproval of some other lot they've never actually met.

And that, ladies, gentlemen, and assorted survivors queuing quietly in the drizzle, is the true secret of human cooperation. We were never going to unite over shared values, survival, or common sense. We were always going to unite over having a good moan about someone else. 

Civilisation may be over. But our capacity for a well-organised grudge? That's what's inheriting the earth. Mind the puddle.