Justin King has picked his moment to leave supermarkets stage

Outlook Timing is key for all the best showmen. And there are few better in front of a crowd than Sainsbury's Justin King. His exit in July could prove his canniest act yet.

Sainsbury's like-for-like sales have ground to a halt, Lidl and Aldi are pulling in the middle classes in ever bigger numbers, a supermarket price war is on its way and interest rates will rise within a year. Tesco, for all its troubles, is far ahead on convenience stores and online, where the growth is.

It's a long term, and risky, turnaround play, but surely Tesco is a better investment than Sainsbury. Perhaps that's why, for all the narrative that Tesco is in decline and Sainsbury's is on the up, Sainsbury's shares are still cheaper, relative to earnings.

Such weaknesses get overlooked in the sparkle of Mr King's presentational panache. His understudy Mike Coupe had better start pointing them out sharpish, or he'll end up copping the blame.