A couple of autumns ago, after a week in Spain where excellent fish and shellfish are considered an everyday necessity, I all but lost interest in buying fish here. The Spanish fishmonger’s regard and care for his produce was evident on every iced tray. In a Madrid market, the Saturday I left, there were 10 sorts of fresh prawn – most sold alive (rising to the equivalent of £65 kilo for the very best). In a comparable London market three days later, there were two – shell on or shell off – both frozen.