The highest sales growth was in electrical goods, with sales 102% higher than the previous year, according to the IMRG Index, which records UK online retail sales.
July's 80% year-on-year growth is in stark contrast with the average of the preceding 12 months, of just 36%.
Ulric Jerome, Pixmania's managing director for France & Northern Europe, said: "June and July are key months for sales of electrical products on the internet, as people buy electrical goods for their summer holidays: digital cameras, MP3s, laptops.
"Since the beginning of the year we have seen that confidence in internet shopping has reached a very high level in the mindset of consumers."
Online clothing sales were 56% higher than a year earlier, reaching a record high, with growth of 1,587% from February 2001 to July 2007.
Factors contributing to July's strong growth included the wet weather encouraging people to shop online, many new-season catalogues being published, and new or updated websites with greatly expanded product ranges.
James Roper, IMRG's chief executive, said: "July's extraordinarily strong market growth spotlights the high level of consumer demand, and yet we are really only just beginning to see basic facilities arriving, and still have nowhere near enough capacity to meet shoppers' appetite for e-retail."