Online sales in 2009 were 21 percent up on the previous year, according to Retail Decisions.
According to the fraud prevention firm, online purchases by around 33 million consumers in 2009 accounted for £49.8bn. Furthermore, 30 percent of all online sales for the year took place in November and December.
Carl Clump, CEO of Retail Decisions said: "In the UK, Monday December 7 (dubbed Cyber Monday) was the biggest online shopping day of the year".
Retail Decisions also said that for the first time in the UK, a post Christmas Monday, 28th December, made it onto the list of top performing online days.
"Mondays are the busiest online shopping days due to consumers' price sensitivity. Shoppers spend their weekends shopping on the high street, finding the items they want to buy. Then they take to the internet to find the best deal they can for their chosen items," added Clump.