It has estimated that Â£5bn will have been spent in Britain's shops over the weekend, as millions of people stocked up on food, drink and presents.
The BRC says many shoppers waited until the last minute to pick up a bargain.
Meanwhile, several retailers are reportedly bringing their online sales forward to Christmas Eve.
High streets, shopping centres and supermarkets were reportedly packed with shoppers on the last few trading days before Christmas.
Many retailers have already started discounting products in advance of the traditional "Boxing Day" sales.
Saturday was expected to have been the busiest day of the year on the high street, with credit card company Visa Europe predicting more than 31 million transactions.
Richard Dodd, head of media and campaigns at the BRC, said: "People have left it very late this year because of their reluctance to spend.  They are holding out for bargains.
"It's been a very busy weekend which will be crucial to delivering a Christmas that is acceptable, rather than exceptional," he added.
Supermarket chain Sainsbury's said the hour between 12:00 and 13:00 GMT on Sunday was its busiest hour ever in terms of the number of customers served.
The company said it expected to sell 225,000 bottles of champagne, 56 million mince pies, 52 million Brussels sprouts and 6,500 tonnes of potatoes over the festive period.
Traders in London's West End had predicted that one million people would shop in the area during the three days leading to Christmas Eve, spending an estimated Â£100m.
At Brent Cross shopping centre in north London, 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.
Elsewhere, Bluewater shopping centre in Kent expected more than 275,000 shoppers to pass through in the days before Christmas Eve, while Birmingham's Bullring centre predicted it would welcome about 340,000 consumers.
Bullring 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 despite optimism in some quarters, 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 to Christmas 2011.
A cold and wet start to the winter could also be taking its toll on the number of shoppers visiting town centres, the LGA concluded.

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Darren McCurry and Peter Harte led the charge with a combined total of 10 points as the Red Hands recovered from a slow start to triumph at Clones.
Mickey Harte's holders will play Derry at Pairc Esler on Saturday in a repeat of the 2016 final.
Derry saw off Monaghan 2-12 to 1-13 in the other semi-final at Armagh.
Fermanagh started the game with a flourish, driven by energy and desire, and they ran at the Tyrone defence at every opportunity, using support runners to stretch their opponents.
They went ahead through Eddie Courtney and Tomas Corrigan, and the Tyrone defence was under sustained pressure.
Midfielder Eoin Donnelly charged through with a goal on his mind, but he was denied by a superb Peter Harte block.
Tyrone finally got their opening score in the 10th minute when McCurry split the posts, and Niall McKenna brought the holders level moments later.
The Tyrone defence grew in stature as the game wore on, and restricted the Erne men to just one point in the second quarter, a third free for Corrigan.
An injury to Colm Cavanagh saw older brother Sean enter the action on the half-hour for his first appearance of 2017 and the beginning of a 16th season in the Tyrone county colours.
Harte's fourth free sent Tyrone in with a 0-7 to 0-4 interval lead, and they started moving more freely in the second period, with McCurry taking over the free-taking  duties, as well as adding a magnificent effort from play.
They went ahead by 0-10 to 0-5 and, after Paul McCusker had pulled back an Erne point, the Red Hands went 0-13 to 0-6 up, with McCurry, Cathal McShane and Lee Brennan hitting the target.
Fermanagh introduced Sean Quigley, who landed a couple of long range frees, with Aidan Breen and Corrigan also on target, but the holders held out for a place in the final.
Christmas sales figures are likely to be "acceptable" rather than "exceptional", the British Retail Consortium (BRC) has predicted.
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Tyrone overcame a stubborn Fermanagh side 0-14 to 0-11 to reach the Dr McKenna Cup final and stay on course for a sixth successive title.