The UK bakery chain Greggs was offering free samples of its vegan sausage roll to early morning punters this week. A friend picking up a coffee declined the offer: “Didn’t seem right.”

He is not with the zeitgeist on this one. The number of people in the UK identifying as vegan or vegetarian is rising; the rolls are a best-seller; and the moral high ground increasingly seems to be held by those with plant-based diets. Join them, we are told, and we can save our health and the planet at the same time.

Will we? The truth is that the jury is still out on this one. Take the environment. It isn’t a certainty that a vast increase in plant-based diets would solve all our environmental problems. The carbon cost of industrial cropping is huge: by some estimates, up to 20 per cent of the world’s CO2 output is a direct result of ploughing. And not all methods of animal rearing are equal. Grain-fed animals, raised in desertified feed lots, are environmentally harmful. But any farmer will tell you (I am married to one) that pasture-raised ruminants can help to store carbon in, and preserve the quality of, our vital top soil.