If you are considering becoming Vegan for environmental reasons I would recommend taking some time to study the the facts about agriculture (specifically British agriculture and grass fed rearing systems). Netflix, BBC and Channel 4 are pretty bias and they base a lot of facts on American feedlots.
British lamb and beef production plays an important part in storing carbon (ie Carbon sink), protecting biodiversity and utilising marginal land that cannot be used for arable crops but can grow very good grass. The crops that are fed to animals are only fed to animals because it's not a good enough grade to go into the human food chain (there are different grades of wheat, barley and oats depending on quality). If we all moved to vegan diets, the British agricultural sector cannot fill the demand for food and more and more food will be imported from abroad, increasing not decreasing our collective carbon footprint.
I understand why people feel uncomfortable about the slaughter of animals, I feel that is a much more valid reason to become a vegan than because of supposed effects of British agriculture on the environment. However another point I'd like to make is the welfare standards of British animals is far superior to the rest of the world and Europe. The EU have imposed many regulations in recent years and sadly only the British farms have applied them in many cases ( for example in pig production). To think of them living miserable lives as they wander round munching grass is pretty laughable, they are living in their natural environment and being cared for every day of their lives.
Finally many British farmers operate at a financial loss, for example, in the UK one third of sheep farmers are losing money, another third are breaking even and only the rest are making a profit. I don't know what your thoughts are of our farmers but with such grim financial situations surely they must be doing it out of passion and love for the industry, not to line their pockets.