Consumers are expected to spend almost £1bn through mobile devices during the peak Christmas shopping period this year.

Online spending is expected to hit £4.6bn in the weeks commencing December 3 and December 10, 15% up on the same period last year, according to IMRG and Capgemini’s e-retail sales index.

Spending on mobile is expected to comprise 20% of that figure, totalling £920m.

Mobile spending has accelerated throughout the year. It comprised just 8.2% of total online sales in the first quarter of the year, and is expected to account for 20% in the fourth quarter.

The Christmas fortnight is expected to account for 26-27% of total online sales during the fourth quarter.

Capgemini head of retail and technology Chris Webster said: “The ramp up of online sales rung up by retailers during the peak weeks will be of huge relief following the challenges of the summer period; from spending constraints to Olympic sized distractions. Retailers need to gear up for the twin peaks of online sales in early December and in-store sales which follow.

“We have seen this year, that mobile access is a must have, not a nice to have for retailers, with close to a billion pounds set to be spent via mobile devices this Christmas.”

The two peak weeks are forecasted to hit later this year than last year because pay day for many people will fall after the final Monday in November.

But retailers differ on their predictions for when peak trading days will fall. IMRG’s survey of 25 senior e-commerce experts showed 44% said the week commencing Dec 10 would be their busiest day, while 22% said teh week commencing December 3, and 22% said the week commencing November 26.

EBay expects its peak day to hit on a Sunday and it expects 30% of all purchases made on the site over Christmas will be through mobile devices.

EBay senior director for mobile Olivier Ropars said: “This will be another record-breaking ‘Super Sunday’ for eBay UK with sales volumes around six times as high as on an average Sunday in September.”