Waitrose is storing its back stock in rolling cages other than on shelves at some stores to improve availability. The 'rolling warehouse' system groups stock by aisle to speed up shelf replenishment.

"Almost half of our shops are now using this system and the rest will by the end of November," a spokeswoman said.

One store manager said the amount of back stock had been halved since his store began using the system two months ago.

Meanwhile, new stores are planned in Manchester and Northumberland.