Britons are expected to spend £200 million less in the post-Christmas sales this year as environmental concerns drive down buying.
Some four in 10 UK adults will make the most of sales from Boxing Day, spending an average of £186 each and a total of £3.7 billion, according to Barclaycard.
However, due to concerns about the environment, 62% intend to make fewer purchases, rising to 68% of women.
Almost seven in 10 consumers (67%) also plan to spend less on “fast fashion” because of the potential environmental impact of its production.
The predictions will cause alarm at the end of another tough year for the beleaguered UK retail sector.
Store closures, business failures and job losses have continued as online has continued to drive growth and competition in the sector.
Barclaycard, which processes nearly half of all credit and debit card transactions in the UK, said Boxing Day spending was 4.8% higher in 2018 than 2017, but a record Black Friday this year could mean that shoppers may have already made the majority of their purchases.
Just 33% said they planned to spend more on Boxing Day than they did during the Black Friday and Cyber Monday sales.
Online spending is also predicted to overshadow in-store receipts, with 60% of post-Christmas sales shoppers making the majority of their purchases from the comfort of their homes.
Rob Cameron, chief executive of Barclaycard Payments, said: “Despite Boxing Day remaining a key moment in the retail calendar, savvy shoppers have been planning their large purchases throughout the entire festive sales period, which begins long before December.
“Our data for Black Friday and Cyber Monday revealed a huge jump in transaction volumes this year, so it’s not surprising that consumers expect to have less money to spend after Christmas, so retailers need to take that into account.
“What’s more, our research shows that shoppers are increasingly thinking about how their purchases impact the environment. Forward-thinking retailers should be making a conscious effort to demonstrate their commitment to sustainability, in order to boost their appeal – and their revenue.”
VoucherCodes.co.uk and the Centre for Retail Research have also predicted that shoppers will shun the high street on Boxing Day, with in-store sales set to drop by more than 12% on last year.
The study suggests that in-store spending will total £3.25 billion – a decrease of 12.4% on last year – while online spending increases by 10% year on year.
Consumers had shown signs of “promotional fatigue” for the last two years after the “many” discount events by Boxing Day, including Black Friday.
The report says: “We expect the numbers attending the sales to reduce. However, it is anticipated that average spending per household in the sales will still be around £459.”
Opinium Research surveyed 2,002 UK adults online for Barclaycard between November 29 and December 3.