Shopping on smartphones and tablets accounted for 40 percent of UK online retail sales between November 2014 and January 2015, according to the latest figures from IMRG and Capgemini.
The figure is up from 37 percent in the third quarter of 2014, representing the steepest quarterly rise in the use of mobile devices in e-retail since the fourth quarter of 2013, when the figure was 32 percent.
IMRG and Capgemini said that confidence is growing in the use of smartphones for online shopping, accounting for 25 percent of the sales made through mobile devices compared with 75 percent for tablets.
A year earlier the sales split between smartphones and tablets was 20 and 80 percent respectively.
Tina Spooner, chief information officer at IMRG, explained that smartphones are traditionally used more as research tools for comparing product prices and information, although this is beginning to change.
"The number of [mobile retail] sales completed via these devices has risen from one in five to one in four in the space of a year, and we've seen mobile conversion rates rise significantly over the same period as UK shoppers now clearly feel confident in using smartphones for completing purchases," she said.
Adgild Hop, retail director at Capgemini, added that, while the growth of smartphones as an online shopping medium may be slight, it is significant to the retail sector.
"Over the last few years, retailers have taken huge steps to improve their smartphone shopping platforms, making them more user intuitive and more secure for customers," he said.
"Coupled with greater connectivity, consumers are more confident than ever in using their smartphones to make complete purchases and not just for online window shopping."
This is evidenced by the efforts of clothing brand Fat Face to make its e-retail website more adaptable for use on smartphone and tablet displays.
Hop also explained that, while smartphones evolve in terms of screen size and connectivity, tablets have plateaued as a mobile device and could "merely serve as a replacement to the home PC".
"I don't think it will be too long before smartphones overtake tablets as the prominent mobile shopping device," he said.
"However, the potential impact of the smartphone on the in-store shopping experience will be a key area of innovation and development in the coming months."
Apple and Visa are planning to roll out Apple Pay in Europe, so it seems likely that smartphones will be used increasingly in physical as well as virtual retail spaces.
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