Shoppers are expected to spend £87bn in 2013 following strong growth through the channel over Christmas.

Online retail sales exceeded expectations over Christmas as shopper spend increased 17.5% in December.

According to the IMRG Capgemini e-Retail Sales Index, consumers spent an estimated £78bn online in 2012, up 14% on 2011. In the first half online sales were “typically in the low teens”, with growth accelerating in the second half.

And IMRG forecasts 12% growth for the market in 2013 “as consumers look to get maximum value from every transaction”, said chief operations and policy officer Andrew McClelland.

Sales via mobile devices last year were “particularly strong”, with revenue through the channel soaring 304% on 2011. “As mobile devices proved popular as gift choices this Christmas, it seems likely that we will continue to see very strong growth throughout 2013,” the report found.

However, conversion rates dropped in December as consumers increasingly used the internet as a research tool as part of any purchase decision, whether eventually made online or offline.

McClelland added: “Retail sites can be accessed through a range of devices and in a range of contexts, whether during a commute, in-store or increasingly in front of the TV. Consumers are going to carry out a lot of research prior to making a purchase, so in order to secure their custom the challenge to retailers is around providing both the value and the experience that will make them stand out from the competition.”

Capgemini head of retail and technology Chris Webster said this year retailers will begin to use mobile as the default channel to reach customers and personalise the shopping experience, moving away from desktop sites first.

Shop Direct Group retail and strategy director Gareth Jones said sales across all its brands were up with 37% of all online customer interactions are now via a mobile device.

He added: “Looking back at 2012 as a whole, the big themes of the year were mobile and personalisation and both will continue to be at the forefront of our e-commerce strategy for 2013 and beyond. In particular, the rapid adoption that we are seeing among customers of the more mobile 7” tablet offers exciting new opportunities to connect with customers wherever and whenever they choose to shop.”