The slump is attributed to slow online sales in the travel sector and the collapse of online travel firm Holidays 4U.
British shoppers spent £5.58bn online in July, a 5% increase on June and an 11.5% year on year rise.
The online electricals market reported a 3% year on year decline, compared with the previous year, having grown 17% year-on-year in July 2010.
Home and garden retailers performed well online recording a 27% year-on-year increase compared with slow growth of 8% last year.
Clothing also saw a 25% year-on-year increase in online sales in July.
IMRG says the slow growth was balanced by the high street, which reported a 2.5% month-on-month sales increase in July, driven by food and clothing sales.
Chris Webster, head of retail consulting and technology at Capgemini says: “The slowdown in July shows the internet is not immune in tough times. Successful retailers will need to expand into multichannel and continue to improve customer experience throughout the online shopping processes. Furthermore, with such a successful first half of 2011, it was a tall order for online sales to maintain such rapid growth.”