John Lewis fashion sales dropped 3.5% for the week to 30 June, as shoppers shunned stores during the heatwave.
Overall sales slipped by almost 8% compared to the same week in 2017.
The retailer said the rise in temperatures helped drive sales of warm weather clothing which were up 27% year on year. It was also a record week for sunglasses which were up 79% on last year.
The retailer added that women’s own brand fashion sales were up 18%.