John Lewis's Glasgow and Edinburgh outlets suffered sharp year-on-year falls in sales in the latest week to May 10, as the retailer unveiled a decline of 4.3% across its UK department store business.

Sales in Glasgow were down 16.3% and Edinburgh was off 9.5%, as John Lewis blamed the sunshine for a slide in all but two of 25 department stores in the UK. It did not make any connection at all between the decline in sales and more general signs of deteriorating UK consumer sentiment.

Patrick Lewis, director of retail operations at John Lewis, said: "We always knew the first really hot week would inevitably cause a dip in sales, and so it did. Not surprisingly our customers enjoyed the sunshine, leaving footfall well down in our shops. Comparisons against last year were even tougher as the equivalent week was rainy, causing a sudden lift in the figures against us (comparatives)."

John Lewis's sales totalled £46.98m in the week to May 10, down from £49.08m in the same period of 2007.

Sales at John Lewis's Aberdeen store in the week to May 10 were down only 1.3% on the same period of last year, making it one of the best-performing outlets.

The only two John Lewis department stores which did not suffer a fall were Knight & Lee in Hampshire and Oxford Street in London, which enjoyed strong advances.

While John Lewis blamed the sunshine for the fall in sales at its department store business, it cited the beneficial impact of the weather on its upmarket Waitrose supermarket chain. Sales at Waitrose in the week to May 10 were up 7.8% year-on-year. This enabled a 2.9% year-on-year rise in overall sales at the John Lewis Partnership in the week to May 10.

Mark Williamson, supply chain director at Waitrose, said: "Summer arrived and sales soared as we hit our targets for the week aided by excellent sales of barbecue lines, beers, salads and suntan lotion."

Patrick Lewis, in contrast, appeared to be hoping the weather would break.

He said: "We have slightly lighter figures against us (2007 comparatives) for the next two weeks. If the weather breaks at the weekend, we'll be more than ready to race back into the increases."