Fashion sales at John Lewis plummeted 7% during the week to July 23, as hot temperatures deterred shoppers from the high street.
Total sales at the department store group were down 4.3% for the week to £73.3m.
Barry Matheson, director of retail services at John Lewis, said: “The hot weather which settled over the UK last week resulted in a slowdown in sales as Britain basked in the heatwave. It had a bigger impact on the fashion and home categories as customers chose to make the most of the British summer.
“A dip in footfall meant that big ticket items had a slower week in home, and fashion numbers were dampened by a drop off in schoolwear purchases as the summer holidays begun.”