Web sales in the United Kingdom increased 7% year over year in the first quarter, the first time quarterly growth of online sales has been limited to single digits, according to the latest from U.K. e-retail association Interactive Media in Retail Group, or IMRG for short, and technology consultancy Capgemini. Last year, first-quarter year-over-year growth reached 17%, which was the strongest Q1 growth since 2011, the two groups say in today’s report.

As is usual, the IMRG Capgemini e-Retail Sales Index includes no monetary figures, only percentages.

The most recent report credits mobile commerce with driving much of the e-retail growth in the first quarter. Mobile sales via tablets or smartphones increased 38% in the first quarter of 2015 compared with the same period in 2014.

“The influence of sales via a tablet or smartphone, which are in effect the main vehicles for growth in the index, is a clear indication of just how valuable mobile platforms have become to the retail customer experience,” says Adgild Hop, principal, head of retail consulting for Capgemini. “If it weren’t for mobile, the overall trends for e-retail would be neutral at best. Retailers therefore need to expect that as online propositions become increasingly commoditized, the secret to differentiation and competitive advantage increasingly resides in the mobile customer experience.”

In March, mobile sales increased 46% year over year, in part due to consumers buying gifts for Mother’s Day, which took place on March 15 in the island country that had once served as the mothership of the British Empire. In fact, that holiday led to a 20% year-over-year increase in March in online sales of gifts in the United Kingdom, the report adds. The report also finds that online travel sales increased 18% year over year in March as well.