High street footfall for the Boxing Day sales fell by 5.9% on last year as the number of shoppers hunting for bargains on Christmas Day rose, figures show.
The high street suffered the biggest decline in shopper numbers, but shopping centre footfall was also down 3.5% while the number of bargain-hunters who ventured out to out-of-town locations fell by 2.1%, according to monitoring service Springboard.
Average footfall across all UK shopping locations was down 4.5% on the same 24-hour period last year as retailers faced "challenging" trading conditions, Springboard said.
The figures suggested that sales would be lower this year on what was traditionally the key shopping day of the year.
Diane Wehrle, insights director at Springboard, said: "This undoubtedly reflects the extent of discounting that has already occurred - particularly over Black Friday - and also the growth in online trade this year.
"In addition to this, Black Friday now rivals Boxing Day in terms of the volume of footfall generated and so its influence as a key trading day in the retail calendar has been diluted."
Selfridges said footfall did not drop but the department store's website had its biggest Boxing Day sale with more than 1.2 million visits, a 15% increase on last year.
Meanwhile e-commerce analysts PCA Predict found that online sales between midnight on Christmas Eve and midnight on Christmas Day were up 5% compared with the same time last year.
Chris Boaz, ?head of marketing at PCA Predict, said: "Christmas sales have defied expectation this year, rising by 5%. We've also seen a year-on-year increase of 9% throughout December so far.
"This increase in sales is due to extended sales periods during the 'golden quarter' between Black Friday and Christmas.
"The past few years have seen a steady increase in consumers shopping on their mobile devices during Christmas, which means they can shop to their heart's content without having to leave the dinner table."
Currys PC World said more than a quarter of a million customers logged on in one hour on Tuesday morning, with 63% using phones to place orders.
Consumer appetite for the post-Christmas sales period fell away last year after an extended period of discounting that began well before November's Black Friday.
But thousands still flocked to Oxford Street in central London on Tuesday morning to grab a bargain, with shoppers clutching large numbers of bags from stores like Next and Selfridges.
Queues formed outside the department store from around 2.30am as people waited to get items with up to 50% off.
Jace Tyrrell, chief executive of New West End Company, said: "The Boxing Day sales in London's West End continue to be popular with many domestic and international shoppers out in force.
"Chinese shoppers in particular have helped boost till receipts to £20 million by lunchtime yesterday, with luxury purchases such as handbags and winter fashion in high demand.
"Although footfall was down in single digits on last year we are still expecting solid sales with average spend increasing and over £50 million to go through West End tills, driven by discounts of up to 70%, which will continue through the week."