Is it ethical for vegans to own cats? It’s an interesting question because vegans look set to take over — there are more than 3.5 million now, up from 500,000 in 2016, and a fifth of us say we’d eat less meat if only we could be bothered. Veganism is the life-style choice for the thoughtful and planet-conscious. The only thing more 21st century than veganism is cats.

Cat ownership in the UK is growing at almost as impressive a rate. A quarter of all British adults have cats. There are 11 million of the sinuous little horrors weaving in and out of our homes. More Brits own cats than dogs, which is depressing.

That vegans are often cat owners is a no- brainer. Even if you know nothing about the booming market for vegan cat food or the T-shirts that say ‘Go Vegan Meow’, it’s somehow obvious. Vegans and cats just go together. Both my vegan friends have cats. But does it make sense for vegans to own cats? No, it absolutely does not. It’s demented. I find it fascinating that some of the most concerned and consciously moral people on the planet are also among the most deluded.

Most of Britain’s cats are outdoor cats because their owners want what’s best for them. And they’re right — it is cruel to keep natural-born predators indoors, however many scratching posts you lay on. It leads to stress and obesity, says the RSPCA. As with kids, so with cats, I suppose. But an outdoor cat is a psychotic death machine. Those boneless fur balls you see draped on garden walls in the morning, yawning and snake-toothed? They spent dawn decapitating baby robins. Instagram that. Cats in this country kill more than 250 million small mammals a year — and some 11 million songbirds. In America cats take an annual toll of three billion birds. Whatever you feed them, however much your neighbours feed them, for a cat, no night out is complete without a killing.

‘It’s just nature,’ say cat apologists. ‘It all balances out in the end.’ Except it doesn’t. Cats are an existential threat to some of our best-loved songbirds: starlings, pipits, bunting, warblers, tree sparrows and house sparrows, blackbirds and tits — all in a spiral of decline, all heading for extinction because of our strange passion for cats.

There really is an official and global consensus that this is a problem. If you’re the type to say ‘trust the experts’ and re-post David Attenborough on global warming, you’re honour-bound to hear him out on cats, and David agrees that cats are a serious problem. In Australia, they are such a threat to native birds that there are cat curfews enforced by law. In Canberra cats live hidden away like Wahhabi wives. No domestic cats allowed outside. In late April the Royal Parks conservation officer, a Mr Tony Duckett, broke cover and begged that Britain follow suit. ‘These so-called pets shouldn’t be allowed to roam freely shitting in other people’s gardens and killing birds,’ he said. ‘As well as killing millions of birds they have brought the Scottish wildcat to extinction.’ I expect he’s in hiding now.

Alone among the bird experts the RSPB insists, rather weakly, that cats are not to blame for the disappearance of songbirds. They just kill elderly or sick birds that would die anyway, they say. It seems an eccentric position to take until you begin to consider just how much the RSPB receives from donations, and how many of those bird--loving donors have cats. Just make sure you put out bird food, says the RSPB, that’ll help. Dutifully, I fill my bird-feeders. And in the early morning I watch as the cats on my street slink by, checking on the feeders with a professional eye, the way a poacher checks a set trap.

If you’re a vegan for environmental reasons, if you fret over the bee apocalypse and the loss of hedgehogs and hedgerows, if you sign petitions about pesticides, if you’ve ever even thought about a ‘There is no Planet B’ T-shirt, you should be out and about, leafleting your street, urging people to stop buying cats. No more plastic bags, no more micro-beads, no more cats.

You should be sending all your like-minded friends copies of Cat Wars by Peter Marra, head of the Smithsonian Migratory Bird Center. Marra says that the birds cats kill are vital not just in themselves but for the ecosystem as a whole; they’re the glue that binds everything together, he says. They pollinate plants, spread seeds, control insects and protect environments from the effects of climate change. Oh how we love to blame farming for anything awry in the environment. How much comfier it is to have a distant enemy, a shotgun-owning carnivore, not one who cosies up to us, purring while we watch Game of Thrones. But farmers have changed their ways, they’ve planted hedgerows and wildflower meadows, and still the birds aren’t coming back. Like it or not, outdoor cats, says Marra, are the leading human-influenced cause of dead birds. They’ve contributed to 33 extinctions around the world, and they spread rabies and toxoplasmosis.

It’s a hard truth for a vegan cat-owner to face — not just that your cat is a threat to the environment but that if you won’t consider keeping her indoors you must face the fact that your veganism is a bit of a performance. You’re a vegan because it gives you a chance to demonstrate what sort of person you are to like-minded souls. The crimes your cat commits in the early hours are irrelevant because no one sees. And if you decided, on ethical grounds, not to get a cat at all, who would ever says: ‘Oh well done! What an inspiration you are.’

If government had any balls — if the Green party had any brains — they’d call for a cat curfew here. But I think we’re long past that. More than 11 million voting cat owners? Much better to go after plastic straws.

Does it make sense to own cats if you care about animal welfare? Mary Wakefield is on the Spectator Podcast with cat lover and investigative journalist James Ball to discuss (25:25):