Online shoppers are set to spend a total of £537 million next Monday in what is predicted to be the busiest internet shopping day of the year.
Total spending on Monday, November 29 - dubbed Manic Monday - is forecast to hit the equivalent of £22.4 million an hour, according to shopping comparison website Kelkoo.
But the busiest day on the High Street is expected to be December 18, when 10 million consumers are predicted to make a last-minute dash to buy Christmas gifts at a total cost of £1.1 billion, or £764,000 per minute.
Online sales are forecast to increase by 29% on last year to £11.5 billion, with overall sales set to reach £68.7 billion, an increase of 1.3% or £862 million compared with 2009, Kelkoo said.
The research was carried out by the Centre for Retail Research, which surveyed 50 major retailers.
Online Christmas sales this year are expected to rise by 28.8% (£2.6 billion) to £11.5 billion - equivalent to 17p for every pound spent during the festive period, and reinforcing the importance of the online sector in driving retail growth.
Gifts will account for almost two-thirds of the UK household Christmas budget at £417 (62%), followed by festive food and drink at £177.80 (26%), travel costs (£42.26 or 6%) and Christmas decorations (£36.50 or 5%).
Fashion, including clothes and footwear, will remain the most popular gift category, accounting for £120 or 29% of the household gift budget, while gadgets and consumer electronics will make up almost a quarter (£102 or 24%) of spending, the study found. The other main categories are toys (£75 or 18%) and cosmetics (£35 or 8%).
Kelkoo chief executive Richard Stables said: "This is the most important day in an e-tailers' calendar.
"Online retailers can see sales rise by up to 60% in the six weeks running up to Christmas compared to the rest of the year, and at no time is this more evident than on Manic Monday, when online sales are forecast to peak at £22.4 million per hour."