SOME say the world will end in fire, some say in ice. And then there are others who reckon the world will finish with flesh-eating zombies devouring every human who passes in front of them.

Mike Carey – MR Carey if you want to be formal – may be in the latter camp. It’s Monday afternoon and Carey, who has spent the earlier part of the day working on a comic script and a TV pitch that it’s too early to tell anyone about, is now talking to me about zombies, post-apocalyptic stories, the current vogue for said narratives, free will and determinism. Oh, and Sir David Attenborough.

Carey is the ne plus ultra of zombie authors these days. In 2014, nine novels and a huge tranche of comic books including The X-Men and Lucifer (yes, that Lucifer) behind him, Carey had what you would call a breakout novel. The Girl With All The Gifts rebooted the zombie narrative for the 21st century. Carey offered a vision of a pathogenic virus which turned people into “Hungries”. At the book's heart was a girl, Melanie, who is seen as a monster. Carey’s novel then asked if, in the circumstances, that is really a fair label.

The book has sold some 600,000 copies and last year was adapted into a smart horror movie which featured the twin glories of Gemma Arterton and a post-apocalyptic branch of Timpson.

Now Carey has returned to the world he first visited in The Girl With All The Gifts with a prequel, The Boy On The Bridge. It seems the end of the world hadn’t quite finished with him. “I missed it,” he says simply. “I missed the world.

“It occurred to me that with any novel there are untold stories. There are things you leave in the negative space of the novel, things you imply but don’t tell. And I decided to pick up one of those strands.”

In this case that was a passing mention of an abandoned armoured mobile laboratory, called The Rosalind Franklin. The Boy On The Bridge follows the lab’s journey around the UK in a bid to find a cure for the virus that is turning the human population into cannibalistic meat-eaters. The boy in question is Stephen, who is on the autistic spectrum, and may be the key in the quest for a scientific solution.

Carey’s vision of zombification is an eerie, fungal infestation. Shopping around for a scientific rationale for his “Hungries”, he remembered watching footage of a parasitic fungus called cordyceps in Attenborough’s television series, The Secret Life Of Plants.

“An ant is devoured by cordyceps from the inside and then the fungal sporangium punches its way out through the ant’s head," he says. "It’s terrifying to watch. You realise you don’t need to resort to sci-fi or horror to get images like that. It’s all around us.”

Carey’s two novels run with that imagery, and yet never lose sight of humanity in the process. The question they ask, however, is what constitutes humanity? In Melanie – who does appear in The Boy On The Bridge – he offers us a vision of the post-human. It feels like a new step in zombie mythology.

“I think it was the right time,” he says of his hot take on zombie fiction. “All genres and subgenres move forward in jerky stages. There’s a stage where somebody comes up with the rules and sells an audience those rules. That would have been George Romero for the modern zombie story.

“I guess most classic zombie narratives were about the outbreak, the moment when the dead rise and the world as we know it falls apart. They’re sort of survivalist narratives.

“But then you reach a point where because everybody knows the rules you can sort of say: ‘Well, OK, let’s do something new.'

“The vast majority of classic horror stories are to some extent about the meeting of the self and the other. Therefore, they are about ‘othering’, about the ways we limit the humanity of others through our perceptions and through our beliefs, which feels like a very current issue.”

Well, indeed. Who needs realism when you can couch your worries in horror fiction? Maybe horror is a truer response. “I think whenever I’ve tried to write in a totally realist model,” Carey admits, “I feel like I’m painting in monochrome.”

And how real is realism anyway? When it comes to Carey, the temptation is to trace his concerns back to his own origins in a Liverpool family in the 1960s, a background steeped in religious imagery, but also divided by different religious affiliations.

Is that too much to claim? “No, there’s definitely something in there. A side-effect of living in that weirdly religiously divided house – divided in more ways than one because my dad was a lapsed Catholic – was that I grew up saturated in religion, but also a little bit divorced from it.

“Mum was Anglican. There were lots and lots of Sunday schools, lots of extra-curricular Christian places you could go to for Bible stories. We used to go to all of them because they would give you chocolate or biscuits at the end of the session.

“I grew up loving the stories, but I never invested any belief in them. Their power for me was emotional rather than devotional.”

And yet questions of belief, questions of free will and determinism are woven into so much of his work. It’s even there in his comic books. Well, what else would a comic called Lucifer be concerned with?

Carey says he owes a lot to his years writing comics. In his teens and 20s he tried to write novels only to end up with what he calls “big shapeless bags of story”. It was while working on comics that he began to grasp the architecture of writing.

“I think the most important thing they taught me was how to structure a story,” he says. “So when I came back to writing prose after a decade of writing mainly comics I was better able to use the freedom that prose gives you. Obviously a novel is a canvas of whatever size you want it to be. But you’ve got to have a sense of that structure in order to use that freedom.”

The Boy On The Bridge is the latest evidence of that. It is also the latest in a long line of post-apocalyptic narratives that have been on the bookshelves and in our cinemas in recent years. The end of the world is rather in vogue. What does that tell us about where – and indeed who – we are these days?

“I think we possibly tell ourselves end of the world stories when the world feels fragile and the end feels like a plausible thing,” Carey suggests.

“In the 1970s and 1980s it was nuclear Armageddon that we were afraid of. At the moment actually that’s still a possibility, isn’t it? But we’ve also got the threat to the environment, global warming, resource depletion, financial meltdown. In all of these ways the world feels like a very precarious place.

“But I think there’s something else going on as well, which is when times are hard – and life is problematic for a lot of people at the moment – there is a sense in which the end of the world presents as a kind of holiday, because so many things that trouble us in our day-to-day lives would cease to matter.

“If society falls apart all you have got to worry about is survival. It becomes life or death. It’s so much simpler. It feels like it would be a bit of a holiday. At least at first.”

Maybe, though frankly I’d prefer Majorca myself. Still, when things do go wrong, when the world ends in ice or fire or zombies does Carey want to be around to see it?

“Yes. The one thing that worries me about death is not seeing the end of the story.”

The Boy On The Bridge by MR Carey is published by Orbit, £16.99