I’m a very staunch fan of the Marks & Spencer crisp combo mix, in every flavour (ready salted is the obvious exception, and the Christmas maple bacon is an acquired taste); the fact that some of the shapes are bad (the wheels) and some are magnificent (the shells) only adds to my admiration. It is random reinforcement, in crisp form. Consequently, when I saw an M&S was opening in Clapham Common, south London, I was pretty excited, but I thought it was just big news for me and maybe one or two other bar-snack connoisseurs.

I had reckoned without the TikTok generation, who have lost their minds over the new biscuits. I’d also overlooked the constituency of fancy people, who favour a shop that sells 17 different varieties of apple, and want to see everything in a fridge, even things that........

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