Tim Bonner: Exposing vegan myths is crucial for the countryside's survival

It is no secret that 'assumption is the mother of all failures' yet both Tesco and Oxfordshire County Council have been made to look very stupid this week by assumptions about vegan food. Tesco was hauled over the coals by the Advertising Standards Authority (ASA) for claiming that swapping beef burgers for its vegan 'Plant Chef' burgers "can make a difference to the planet". Unfortunately for Tesco it had not a jot of evidence that this was the case and given that the heavily-processed vegan burgers included ingredients shipped from all over the world, the ASA told Tesco that the adverts must not appear again in their current form. The supermarket must also ensure that it does not make environmental claims about its products in the future unless it holds sufficient evidence to substantiate them.

Meanwhile, in Oxfordshire, the Liberal Democrat, Labour and Green cabinet which runs the County Council decided that it would be a great wheeze to insist that the food provided at council meetings is "plant-based" on the assumption that this is better for the environment. Unfortunately, when a Green councillor tweeted a picture of the first plant-based lunch it included a range of delicacies like watermelon, kiwi and mango which were obviously not grown in Oxfordshire and would have racked up a huge number of food miles. Not only were assumptions about the environmental benefits at least questionable, but the lunch cost Oxfordshire taxpayers £160 more than the month before as well.

These examples matter not because there is any problem with people adopting plant-based diets, but because the assumption that moving from meat to a non-meat diet always provides a benefit for the environment. As Tesco has learned, that is an assumption that cannot just be made. The judgment should not be 'meat bad, plant-based good', but 'locally sourced and sustainably produced good, food miles and heavily processed bad'.

Red meat produced in Britain is among the most sustainable in the world. Despite the endless propaganda, cattle and sheep account for just 3.7 per cent of UK carbon emissions if you include the carbon stored in grassland and, unlike some plant-based products, very little meat consumed in the UK comes from systems that deplete rainforests and generate large amounts of emissions.

Knowing where your food comes from and how it is produced is far more important than whether it is animal or vegetable. Challenging assumptions about the benefits of some plant-based products and the casual denigration of livestock farming matters because, if they are allowed to go unchallenged they threaten the sustainability of both the planet and the countryside.