Bargain hunters who could not wait until the traditional Boxing Day sales opened were busy online during Christmas Day, say retailers.
Sales in store begin on Boxing Day
The Marks and Spencer website reported busy traffic soon after its online sale started at midnight on Christmas Day.
While clothing were popular purchases, other online shops predicted TVs and laptops would be snapped up.
A Post Office survey of 2,042 people suggested one in five Christmas Day web surfers would buy something online.
A spokeswoman for M&S said the company was expecting at least 200,000 shoppers online for Christmas.
Electrical retailers PC World and Currys, as well as general retailer Argos, began their online sales on Tuesday as well.
Sales start in PC World and Currys digital stores on Boxing Day and in Marks & Spencer stores from 27 December.
Comet was expecting most Christmas traffic in the evening, with a spokesman saying: "It really seems that, regardless of the family get-together, people are keen to bag themselves a bargain ahead of the Boxing Day rush."
It was a sentiment echoed by Post Office Broadband manager Stewart Fox-Mills, who said: "Whereas families traditionally fought over the TV remote control on Christmas Day, the growing popularity of computers and the internet means more people will be fighting over the mouse this year."
Before Christmas, the British Retail Consortium said there had been a seasonal rush in the preceding 10 days.
As a result, sales will be up on 2006 and retailers are due to beat last December's year-on-year growth.
But heavy discounting had tempted shoppers in, but retailers would have seen "margins squeezed in a crucial month".