Online retailers are preparing for strong spending as the Christmas shopping peak approaches, with consumers forecast to spend £4.6bn online over the two weeks commencing 3rd & 10th December according to IMRG and Capgemini.

Just under a billion of that figure is expected to go through mobile devices, 15% up on the same period last year.

IMRG says that mobile retail sales have accelerated over the course of the year, as consumers become more comfortable using their smartphones for Web browsing and shopping. In the first quarter of 2012, 8.2% of total e-retail sales were made through a mobile device.

"By the end of the fourth quarter we anticipate that figure will have reached around 20%," states the retailer group.

The two peak weeks of online shopping activity are expected to account for 26-27% of total e-retail sales during the final nine weeks of the year, making up £4.6bn of the total £17.4bn forecast for the period).

Tina Spooner, chief information officer at IMRG, comments: "While it is still common for consumers to browse the shops at weekends before making the final purchase online at Monday lunchtime, we are increasingly seeing the popularity of 'second-screening', where people browse on their mobile devices in front of the TV. Our recent research with eDigitalResearch found 80% of smartphone and tablet owners use their devices in this way, so we can expect to see that 20% share continue to grow in 2013."

Online flea market eBay expects that 30% of of all purchases made on the site this Christmas will be through mobile devices.

Olivier Ropars, senior director, mobile, eBay says: "The high street as we knew it, where the 'showroom' inside the four walls of the store was the centre of our shopping experience, has transformed forever. Consumers now carry a global store in their pocket allowing them to shop anytime, anywhere."