At Shambala festival, during the hottest bank holiday on record, peace and love is about to turn sour. I am standing next to author Louise Gray, who is here to talk about wild alternatives to mass-produced meat. The cricket brownies are baked; we have been skinning squirrels and marinating them in satay, then decided to unwind by checking out a punk-reggae band in a nearby tent. That is when the singer announces his feelings about her presence there. “Last year this festival was 100% meat- and fish-free. Now they’re saying we should eat pests and squirrels,” he spits. “It’s 2017. If you’re still eating the dead bodies of animals, you need to check your fucking privilege.” The crowd cheers. I am worried we are about to be ethically eaten alive.

In the wake of The Ethical Carnivore, her award-winning account of the year she spent eating roadkill and animals she had killed herself, and investigating abattoirs, Gray received death threats and abuse. Images spring to mind of balaclava-clad activists chucking red paint and righteous invective. “If it comes down to it, I am not with you,” I tell her, gallantly.

‘If we want to eat meat, the argument to get it from animals such as grey squirrels is persuasive.’ Photograph: Dan Farrell

The friction is hardly surprising. Shambala is a hippy sort of place, with as many recycling points as there are naked people painted blue, which is a lot. Ravers have to carry their own cups, and food stalls are entirely vegetarian. On the festival’s Facebook page, protests over Gray’s talk quickly escalated into an argument about speciesism, human immigration and genocide. Onstage at the Garden o’ Feeden – the festival’s food and debate tent – the edginess is palpable.

“Let’s hear her out and fight afterwards,” the host pleads. In a craven attempt to fit in, I am wearing a full-length dress and Carmen Miranda fruit hat; Gray has nowhere to hide.

The debate around eating meat is hard to progress intellectually – you either believe on some level that it is a natural part of the cycle of life, or an unnecessary moral wrong. Gray, the daughter of a farmer, is here to argue for an ecological, flexitarian position between the two.

Our current production model is energy-intensive, wasteful, cruel and unsustainable. We should be eating far less meat, and thinking more about it. Her book describes the year she spent eating only animals she had killed herself – a common, if hypothetical, answer to the abstraction and scale of the mostly invisible meat industry. She cried after killing the first rabbit, and talks about her ambivalence at stalking and shooting a red stag. The responsibility of taking an animal’s life bears an emotional cost, she tells the crowd. “It’s pretty intense.” It is also not something one can practically do in a city (unless you maybe fancy the urban equivalent of turducken, eating a fox that recently swallowed a pigeon, which last dined on KFC).

Yet there is a lesser explored alternative to factory meat, besides insects, roadkill or hunting your own: a diet of invasive species. I know what’s coming: backstage I watched Gray skinning a bag of grey squirrels, carefully stripping pelts from flesh, cleaning out shot and slicing meat from bone. Several vegan chefs walked past, all of them fascinated, though one declared: “Bit Hunger Games, innit? Or Winter’s Bone. Something with Jennifer Lawrence. Christ, I wish I hadn’t seen that.” She means the flayed legs of the skinned critter in front of her, rather than the film.

Out front, Gray’s cousin has been standing sidestage to provide security/hand out brownies. She presents us with a plate of grilled sticky squirrel skewers, which are passed around. I try one, then a few. Surprisingly, many others in the crowd do the same. The plates disappear. The flavour is potently gamey, not a bad accompaniment to the zesty lime and creamy satay. I have certainly eaten worse on a cheap pizza. The hair that sticks to my teeth is off-putting, though.

These squirrels are from Dumfries and Galloway, home to one of the few surviving red squirrel populations in the country, maintained by controlling greys. If we want to eat meat, the argument to get it from animals such as grey squirrels is persuasive. They are wild, organic and definitely free range. As with insects, the “ick” factor might just be something we have to get past.

This is the part of the message “Crayfish Bob” Ring has been trying to get out. A grizzled trapper of 15 years’ experience, I met him earlier at a picnic table outside the tent, smoking a roll-up pensively and squinting like Captain Quint. His passion is removing American crayfish from British waters and selling them at his restaurant pop-ups. The lobster-like signal crayfish were introduced in the 1970s to be a lucrative export to the Scandinavian market (which was soon dominated by cheaper imports of Chinese crayfish). The collapse of the scheme saw them escaping the fisheries, passing a deadly plague on to smaller, native white-clawed crayfish and destroying their numbers. The voracious predators eat fish and amphibian eggs, out-compete other species for habitat and burrow into river banks, causing their erosion and collapse. Crayfish Bob describes how they travel the country using the waterways, by hanging on to barges. I feel very conscious I’m wearing a tutu.

“I’ve gone into this business with the objective of going bust due to lack of stock,” he says vehemently. “I would get so much satisfaction from getting rid of them.” Neither Gray nor Crayfish Bob think eating grey squirrels or signal crayfish would make a dent in their numbers – the species are here to stay, and their realistic concern is to level the ecological balance. The EU list 37 alien invasive species, including muntjack deer, Ruddy duck and Siberian chipmunk. Legally, the crayfish have to be controlled anyway, Ring reminds me, so are not being bred or killed primarily to be eaten. After he realised the scale of the problem, he founded the National Institute of Crayfish Trappers, and became Crayfish Bob, selling gumbos and crawfish boil. “I’ve had vegetarians come up to me and say: ‘What you are doing challenges all the reasons I became vegetarian.’ They see it as a way they can eat some fish.”

‘In a craven attempt to fit in, I am wearing a full-length dress and Carmen Miranda fruit hat; Gray has nowhere to hide.’ Photograph: Dan Farrell

Of course, vegetarians who feel killing animals for any reason is wrong won’t be convinced. Back in the tent, Dr Amelia Roberts, a member of Animal Aid and an animal rights advocate, is pushing back on a number of Gray’s points. Like many, she believes the American grey has been scape-squirreled. She cites evidence that the decline of their red cousins is mostly due to loss of habitat, a problem caused by people. And the fact is all invasive species were brought here by humans, something the rhetoric of the argument tends to obscure. Nonetheless, she says she agrees with 90% of what Gray has been saying, which seems positive.

After a lot of whoops and applause, Gray is relieved the talk has gone down well, like the satay. I am surprised when she announces that the festival should be totally vegan next year “It’s the most inspiring thing they could do.”

She is all for people eating better meat, speaking to livestock farmers and being more conscientious. But she wryly acknowledges the difficulty in being an ethical meat-eater, especially in a market-led society that makes it difficult. “You can’t poke around people’s houses when you go around for dinner, or ask them to pick the label out of the bin. It is probably easier to just be vegetarian.”