Cutting domestic farm subsidies is one of the most pressing subjects for trade ministers meeting in Geneva today to rescue the crisis-hit Doha round of global trade talks. But though it will affect millions of farmers around the world, the subject is as arcane as it is important.

Its astonishing complexity recalls the remark made by Lord Palmerston, the 19th-century British foreign secretary, of an intractable European diplomatic puzzle known as the Schleswig-Holstein Question. Only three people had ever understood it, he said, of whom one was mad, one was dead and the third, Palmerston himself, had forgotten.