Last December the level was 5.6% and it has risen steadily throughout the year to reach 12% in October.
Mobile sales reached a high of 11% of all online sales in October, up from 3.1% in the same month last year.
IBM claims the growing popularity of mobile devices including iPads and iPhones is driving the trend.
Research shows conversion rates on iPads are higher than other mobile devices because of the ease of online shopping on the tablet device.
In addition, iPhone users account for nearly double the amount of traffic to retail sites from Android users.
The average conversion rate of those visiting retail sites is 4.7%.
Social media also plays a key part in improving conversion rates with a 7.6% conversion rate from those being directed to a retail site via a social media site.
IBM's enterprise marketing management leader for UK & Ireland Andrew Jackson-Proes said: "Retailers must invest in highly personalised, customer-loyalty building systems that catch the attention of price and promotions-sensitive customers at exactly the right moment and on the right channel."
The study also suggests shoppers are taking advantage of online discounts as retailers launch seasonal promotions earlier than usual; sales in November are expected to grow by 10% year on year.
Data for the survey is collected from the websites of more than 150 UK retailers to discern online trends.
Follow Matthew Chapman at @mattchapmanUK