Up to 14 million bargain hunters are poised to set a Boxing Day record and splurge £3.1billion in the sales.
With prices slashed by up to 90%, diehards will queue from midnight to be first to bag sales deals as stores like Next opening from 6am.
Another 11 million will avoid the crowds and log on to bag online bargains.
While stores slashed prices by an average 50%, early birds were set to snap up even bigger bargains such as a Planet lace black jacket knocked down by 90% from £299 to £29 at Debenhams.
The department store has £144million of savings on big brands like Hugo Boss and Yves St Laurent and in-house designers including Betty Jackson and Julien Macdonald.
Argos slashed prices by up to 64% and Marks & Spencer has half price bargains.
Today’s spree is expected to top last year’s £3.08billion with the nation set to blow £2.24billion in stores and £856million online, according to the Centre for Retail Research.
Fenwicks opened for the first time on Boxing Day and London’s West End is on course to take £100million over the weekend.
Jace Tyrrell, of the New West End Company, which represents 600 retailers, said: “A number of luxury stores on Bond Street will open for the first time on Boxing Day.
“We expect international shoppers to lead the spending.”
More than 350,000 shoppers are expected today at Westfield London and Westfield Stratford, with 250,000 at Cardiff’s St David’s centre and 230,000 at Birmingham’s Bullring. Bluewater, Kent, is set to see 160,000.
And 160,000 will head for Sheffield’s Meadowhall, 130,000 to Lakeside, Essex, with 100,000 at Bristol’s Cabot Circus.
Scottish malls expect 120,000 at Braehead 100,000 at Glasgow’s Silverburn and 80,000 at Aberdeen’s Union Square.
Professor Joshua Bamfield, of the CRR, said: “Some shoppers left Christmas late and did not find items they wanted.
“Others have switched to post-Christmas to take advantage of bigger sales.”