Justin King is sounding typically confident. After revealing strong sales figures and aggressive expansion plans, the chief executive of J Sainsbury is grandly insisting that he does not dwell on how rivals are performing. “We don’t spend a lot of time thinking about the relativity of our position,” he says.

That lofty view is not widely shared. In the fiercely competitive supermarket sector, each quarter’s underlying sales figures are scrutinised for the slightest changes in the pecking order.