Sales at John Lewis fell 0.6% year on year to £68.6m in the week to August 8 due to patchy summer weather and the impact of the tube strike on London trading.
However, fashion outperformed the other product categories, with sales up 2.9%. Womenswear sales grew by 14.8% and menswear by 6.1%.
Online sales increased by 8%.
David Barford, director of selling for London and the South, said: “Summer continued to show itself periodically and trade in London was hampered by the tube strike, along with the comparisons of some key sporting events in the Southeast last year.
“Looking ahead we have the first groups of holidaymakers coming back and looking for back-to-school inspiration and the next wave of people off on holiday. We have plenty of opportunity to make up some lost ground from last week and to optimise all areas of our offer.”
London Underground workers have been on strike twice in the past six weeks and are planning more action on August 25 and 27.
Research from the British Council of Shopping Centres found that the August 6 strike reduced footfall at London’s shopping malls by 8.7% compared to last year.