Photo by Jeff J Mitchell/Getty Images It was predictable, and indeed predicted. There has been no shortage of nutty policies unveiled by Scotland’s political parties during this election campaign, and the SNP’s proposal to cap supermarket food prices is right up there with the maddest. Retailers have reacted as you’d expect them to: badly. Lawyers have questioned the Nats’ ability to intervene in the way they intend. It’s been pointed out that UK food prices are already among the cheapest in Europe due to the hyper-competitive market place. As I wrote previously when the policy was announced, it failed the sniff test: a bad idea in theory and practice, destined for the bin. Nothing that has happened since has changed my mind. Last week, a shaken John Swinney appeared ready to make a swift U-turn when he said he would consider a voluntary scheme instead. Then he U-turned on the U-turn, insisting he would push ahead with his plan to regulate prices if supermarkets didn’t act first.…