Retailers are hoping for a surge in spending on Saturday as the recent run of cold weather forces hordes of last-minute shoppers out for Christmas gifts and groceries.
Some 17.4 million shoppers are expected to spend £1.6 billion on last-minute festive purchases on "Super Saturday", according to predictions from Voucher Codes and the Centre for Retail Research.
December 22 is the first time in 11 years that the last full shopping day before Christmas has landed on a Saturday, and coincides with many workers receiving their pay checks the day before.
Last year, the same date fell on 'Frenzied Friday' when 15.6 million shoppers splurged £1.1 billion on the high street and online.
Almost half of Britons (43%) plan to leave their Christmas gift shopping to the last minute, a separate survey by VoucherCodes and Opinium found.
Paul Lewis, senior director of marketing at VoucherCodes, said: "With Christmas falling on a Monday this year, Saturday will be particularly busy on the high street as Brits brace the busy crowds to snap up last-minute festive purchases.
"A number of retailers will also be bringing their Boxing Day sales forward this year, so Brits should head online to check out the great savings to be made on bigger ticket items including electronics and home appliances."
An analysis of spending patterns by payments processor Worldpay suggests high streets could be at least 45% busier this weekend than usual.
It also expects Saturday to be the busiest shopping day of the season.
Worldpay chief marketing officer James Frost said: "It would be easy to underestimate the importance of this weekend in terms of the retail calendar. December 23 is always one of the busiest shopping days of the year, but in other years a lot of that spending will come from food and grocery as people get ready for a Christmas Day feast.
"The way Christmas has fallen this year however, added to the impact of the recent cold snap which saw many consumers stay at home, means shoppers are far more likely to take things right to the wire when it comes to buying gifts.
"The overall result of this is a kind of 'double whammy' effect, which should contribute to an extraordinary day of spending."
:: Opinium surveyed 2,005 UK adults online between October 12-17.