The traditional Boxing Day sales have been brought forward to Christmas Eve as dozens of retailers seek to out-do each other and win customers' hard-earned cash.
Last-minute bargain hunters will be able to cash in on internet sales from noon as online retailers slash their prices earlier than usual.
The Marks & Spencer online sale sale begins at noon today, with John Lewis following suit at 5pm and Currys/PC World at 7pm, the Daily Mail said.
Online giant Amazon will start is sale on Christmas morning, a day earlier than usual.
High street retailers were hampered yesterday as Sunday trading laws restricted them to opening for just six hours.
Supermarkets, shopping centres and high streets up and down the country were crammed with people on the last few trading days before Christmas.
Sainsbury's reported its busiest ever hour in terms of customers served from midday to 1pm yesterday, while 35 branches opened at midnight and will trade until 6pm today.
One million visitors were expected in London's West End during the three-day period from Saturday to today, during which over £100 million was expected to be spent.
Some 400,000 men are predicted to flock to the area today in a rush to grab last minute presents for their families and loved ones.
The British Retail Consortium predicted there will have been £5 billion of retail spending over the weekend.
Richard Dodd, head of media and campaigns, said: "People have left it very late this year because of their reluctance to spend - they are holding out for bargains - and we've had a final weekend just before Christmas.
"It's been a very busy weekend which will be crucial to delivering a Christmas that is acceptable, rather than exceptional."
Supermarket giant Sainsbury's expected to sell 225,000 bottles of champagne at the weekend, as well as 56 million mince pies, 52 million sprouts, half a million kilograms of Christmas cheese and 6,500 tonnes of potatoes over the festive period.
Saturday was expected to have been the busiest day of the year on the high street, with credit card company Visa Europe predicting almost 32 million transactions, with £1.26 billion of spending on Visa cards alone.
A spokeswoman for John Lewis said the retailer experienced a busy weekend, which followed "a great last two weeks".
At Brent Cross shopping centre in north London, bosses said sales were likely to be bigger than ever before.
Centre manager Tom Nathan said the weekend would be their busiest period because schools had broken up late and Christmas Day was on a Tuesday.
Bluewater shopping centre in Kent said Saturday was its busiest day of the year, and expected more than 275,000 shoppers through the doors over the weekend.
Elsewhere, Birmingham's Bullring centre welcomed the hordes and said 340,000 people were expected to visit its stores before Christmas Eve.
General manager Tim Walley said: "This Christmas we essentially have an extra weekend of trading in comparison to December 2011, so we're expecting a bumper weekend."
But the Local Government Association (LGA) said confidence on the high street remained low.
Its annual Christmas survey found that 84% of town centre managers said confidence among shoppers had either not improved or worsened compared with this time last year.
The LGA suggested that the particularly cold and wet start to the winter could also be taking its toll on the number of shoppers visiting town centres.