Because, according to this exceptionally detailed study from 2006, lamb, apples and dairy produced in New Zealand and shipped to Britain have a smaller carbon footprint than the equivalent products produced in Britain. To be exact, the UK uses twice as much carbon per tonne of milk solids produced as New Zealand, and four times the amount as New Zealand for lamb. I was so baffled by the report I wanted to know whether I had read it correctly. I emailed Tim Benton, professor of population ecology at Leeds University who is also the "UK Champion for Global Food Security", charged with co-ordinating work on the subject between research councils and government departments. He truly understands both the global food challenges that we face and what sustainable intensification means. He had been an invaluable source of academic papers and scholarly advice for my investigation into the challenges of food security from the very start. I wanted to know whether the report was simply a function of the New Zealand agriculture sector attempting to protect its commercial interests by ferociously massaging some numbers.

He threw in some caveats but, he said: "The overall picture is probably true."