"A vegan Britain could make a massive contribution to global food stocks. But I cannot advocate a diet that I am incapable of following. I tried it for about 18 months, lost two stone, went as white as bone and felt that I was losing my mind. I know a few healthy-looking vegans, and I admire them immensely. But after almost every talk that I give, I am pestered by swarms of vegans demanding that I adopt their lifestyle. I cannot help noticing that in most cases their skin has turned a fascinating pearl grey."