Online spending in May rose 1.6% to £4.5 billion against the previous month, driven by fashion, footwear and accessories.
According to the IMRG Capgemini e-retail sales index the overall rate of sales growth has slowed but clothing, footwear and accessories sales surged by 4% against the previous month, boosted by the warmer weather.
Footwear sales alone rocketed 17%, ahead of the premiere of the Sex and the City film.
Anthoula Madden, vice president at Capgemini UK's consumer products and retail team said: "Although online sales across the board are more robust than on the high street, falling property prices and persistent news of a credit crunch are causing UK shoppers to become more careful with their disposable income."
Madden said: "The pressure that the current economic climate is placing on retailers is a reminder that e-retailers must become ever more innovative in attracting new customers by providing a truly integrated multi-channel offering to maintain existing customers."
Bruce Fair, managing director of Kelkoo.co.uk, added: "Online fashion and clothing sales have been steadily rising for some time as people try things on at the weekend and buy online during the week. It is also testament to the improved levels of service that web shops are offering and the fact that major fashion retailers are investing in their online properties."
Alison Lancaster, marketing director at Charles Tyrwhitt, said: "We are delighted our web sales continue to show positive double-digit like-for-like growth in today's challenging market. For the month of May 2008, web sales at www.ctshirts.co.uk grew by 10.8% against the same period last year across our three key markets - UK, USA and Germany."