Unseasonably warm temperatures in September hurt U.K. e-commerce sales, says the e-Retail Sales Index from technology consultancy Capgemini and U.K. e-retail association Interactive Media in Retail Group, or IMRG. U.K. online sales grew just 7% year-over-year in September—the slowest growth rate since 2010.

“The unseasonably warm weather last month clearly had a negative effect on the online retail industry, with apparel merchants in particular seeing a significant impact on sale,” says Tina Spooner, IMRG’s chief information officer. Even though apparel and fashion merchants launched their fall and winter lines in September, the above-average temperatures meant that shoppers weren’t ready to think about buying items like boots and winter coats, she says.

Online apparel sales only grew 0.3%—the lowest recorded rate and footwear sales increased just 4.5%. Meanwhile,  accessories sales soared 48%.  The index did not note why accessories grew at a much higher rate.

This month’s index also found that retail chains fared better in the warm weather, with online sales growth of 8% year over year, compared to 5% year-over-year growth for online-only merchants. “This month has also yet again highlighted the relative strength of multichannel versus online propositions, with a year-on-year like-for-like performance for multichannel retailers that is 80% higher that their pure-play online counterparts,” says Adgild Hop, principal, head of retail consulting at Capgemini

And while U.K. consumers continue to shift their shopping sessions to mobile devices, mobile commerce experienced the slowest growth rate ever—29% compared to the previous low of 36%.