Millions of bargain-hunters will splurge £1.65billion on Saturday, making it the biggest shopping day of the year.
Stores have slashed prices by up to 66%, the kind of cuts not usually seen until Boxing Day.
Many are staying open longer, with 11 Primark stores not closing until 11pm.
Malls such as the Trafford Centre in Manchester and Westfield in East London will be trading until 9pm.
Experts say almost 12 million shoppers will be out, spending £2.5 million a minute.
Prof Joshua Bamfield, director of the Centre for Retail Research, said: “People haven’t really had a chance to plan properly for Christmas because of the changing scenarios over the last three months.
“Saturday is all about serious shopping, not browsing.”
Asda has beefed up security, with extra staff at entrances to 421 stores from today until Christmas Eve. The supermarket has launched a virtual queuing app so customers can wait in cars until it’s their turn.
Tesco sparked veg wars by slashing parsnips, carrots and sprouts to 19p per kg.
Asda cut its prices to 20p.
Waitrose is expecting shoppers to make a beeline for the bubbly aisles as sales of pink champagne have already rocketed 36% year-on-year and online searches for alcoholic fizz have soared by 343%.
The four-day spending spree that began yesterday will give the high street a £5.2billion shot in the arm, the CRR said.
According to Office for National Statistics figures, fashion stores were the hardest hit by the November lockdown, down 19% month on month.
Supermarkets were the only winners, with food and homewares sales up 3.1% and 1.6% .
Silvia Rindone, of analysts EY UK & Ireland, said: “Retailers need to evolve to meet seemingly permanent changes.”
