Total sales at Waitrose were 6.4 per cent higher in the third week of May than during the same week in 2010.

The upmarket retailer said it was pleased with the performance. “This was a positive result despite the tough comparison against the equivalent week last year, during which we experienced sizzling weather and sales as shoppers dashed out to buy for impromptu barbecues,” said Waitrose retail director Tony Solomons.

The cooler weather during the week this year prompted shopping patterns more reminiscent of the autumn and winter months as root vegetables had their best week for some time, with sales of carrots and swede up by 18 and 28 per cent respectively.

“We saw a very positive response from shoppers to our latest recipe, Delia's Cheddar-crusted smoked haddock, with eight weeks' worth of smoked haddock, three weeks' worth of Jersey Royals and six weeks of essential Waitrose English mature grated Cheddar sold in the first four days of the promotion,” added Solomons.