Haven’t we been here before? Back in 1988, a Conservative leader, Margaret Thatcher, hit the headlines with an unexpected speech about the threat of global warming. She caught the popular mood: environmentalism was in vogue, epitomised by publication the same year of the best-selling Green Consumer Guide.

Big business sat up and took notice. Tesco, J Sainsbury and other supermarket chains vied to put green products on their shelves – while taking flak from campaigners for promoting consumption instead of reducing it. In 1989, the Green Party scooped 15 per cent of the seats in the European elections. Then the wave broke, recession set in, and more pressing concerns such as unemployment and the UK house price bust took over.