The pyres across Britain shamed humanity. Cows were rounded up, shot in the head and then flung into the flames. Onlookers saw terrified animals desperately trying to escape and being cornered by gunmen. As the death queues stretched out, some of the poor animals were still blinking hours after they were shot. The incinerators worked day and night.

Eventually, 4.4 million cattle were slaughtered this way when BSE – or mad cow disease – peaked in Britain in the 1990s. There were even worse scenes when foot-and-mouth struck here a decade on: more than 10 million animals were culled and incinerated in response.

And now mad cow disease is back: the first case in Scotland in a decade has been confirmed.

The disease first emerged when farmers fed beef offal to cows. Unsurprisingly, it turned out that agricultural cannibalism was a bad idea. Since then there have been some changes to the rules – brains and spinal cords no longer go back into the food chain. But the disease, which cost the UK economy up to £980m last time, has returned nevertheless.

This is not only of concern to cows, farmers and economists – BSE could kill you, too. If you eat contaminated beef, the human form of the disease can progressively attack your brain and eventually overcome you. It's thought that at least one in 2,000 people in the UK is a carrier of the disease, which can remain dormant inside you for over a decade.

I wonder how much clearer it needs to be that eating meat and consuming dairy products is a bad idea. Just last week, the most comprehensive analysis yet of the food system’s impact on the planet found that huge reductions in meat-eating are absolutely essential if we are to avoid environmental Armageddon.

Scientists agree that the meat and dairy rackets are destroying the planet – the top five firms alone are already responsible for more emissions than other major polluters like ExxonMobil, Shell or BP. The United Nations says that the animal agriculture industry is responsible for more greenhouse gas emissions than the combined exhaust from transportation.

This farming is also responsible for huge emissions (73 per cent in the US) of nitrous oxide, a gas that is 310 times more powerful than carbon dioxide in trapping heat in the atmosphere. And unless we change our eating habits, it’s only going to get worse: emissions for agriculture are projected to increase by 80 per cent by 2050.

From this perspective, it no longer matters whether you think factory farms are cruel, or inhumane, or whether you think it’s OK to slaughter animals. Whether it’s through BSE or environmental disaster, the meat and dairy industries, which between them kill 70 billion animals each year, are still major threats to your life and your way of life.

And as supermarket chains slash margins to offer you discounts, farmers feel forced into cutting more and more corners.