“Who’s having a #meatfree Monday?” So asked Waitrose in a tweet last week, offering up a recipe for its McCartney-inclined followers.

The most perplexing thing about the ‘pithivier’ it suggested wasn’t the mystery of what a pithivier is (Waitrose shoppers know their posh French pies), but that it contained squash, mushroom and… ham. Oops!