Bargain hunters started queuing early this morning for the Boxing Day sales as experts say they expect 22 million people to hit the shops today.
Shoppers eager to grab the best deals snaked round the block outside department stores waiting for them to open.
Millions are expected to hit the high street and spend as much as £3.74 billion as stores reopen for the Boxing Day sales.
While many big name retailers launched their sales online on Christmas Eve, the high street is hoping for record footfall today.
Figures from VoucherCodes.co.uk and the Centre for Retail Research suggest 22 million shoppers are set to spend £3.74 billion in the Boxing Day sales - a 6% increase on last year.
In good news for the high street, the research predicts that 78% of total Boxing Day transactions will take place in bricks and mortar stores.
Online sales are set to be up 13% on last year.
VoucherCodes managing director Claire Davenport said: "While pre-Christmas sale dates have soared in popularity over the last couple of years, it seems they are yet to take over our more traditional savings days, with many retailers choosing to go all out on Boxing Day, running deals as early as Christmas Day right through to the start of the New Year.
"Judging from our research, it looks as though consumer appetite to snap up deals is here to stay, both on the high street and online."
Department stores Harrods, Selfridges, Liberty and House of Fraser are offering designer goods at a fraction of their usual price, while both Next and Marks & Spencer have launched discounts of up to 50% on sale items.
Retailers across London's West End are preparing to take over £100 million in sales over the next three days.
A number of Bond Street stores will open on Boxing Day for the first time as a result of it falling this year on a Saturday rather than a public holiday.
Fenwick department store on Bond Street will open for its first Boxing Day in its 124-year history.
Steve Richardson, UK regional director at analysts FootFall, said: "With Boxing Day falling on a Saturday, this means for most an extended Christmas break with the extra bank holiday on Monday.
"We anticipate the extra day will motivate shoppers to use this additional day off to seek out further bargains, spend Christmas vouchers and even return or exchange unwanted Christmas gifts, causing shopper traffic to rise 3% year-on-year on Boxing Day."
Usdaw general secretary John Hannett urged shoppers to respect store staff "every day, but particularly during the Boxing Day sales when bargain hunting can turn into a frenzy".
Online shoppers are expected to spend £856 million today, up 22% on last year's £699 million, according to data firm Experian and online retailing trade association IMRG.
Steven Madeley, general manager for St David's shopping centre in Cardiff, Wales, said he is expecting thousands of shoppers.
He said: "At peak times, we've seen Welsh shoppers spend around £2 million a day at St David's, and over one million visitors a week.
"High tech gadgets and beauty have performed particularly well, and we expect savvy shoppers to get some great deals over the coming days. Some of our stores even closed early on Christmas Eve this year to prepare for a busy Boxing Day.
"The last few years have seen even more shoppers visit on 27 and 28 December – we're expecting the coming days to be very busy at St David's."