Retailers are hoping for a last-minute Christmas sales rush as shoppers make up for delays caused by the extreme weather.
The looming VAT hike is also expected to send consumers searching for big-ticket items this month, with tomorrow predicted by payment card group Visa Europe to be the busiest ever shopping day in the UK.
Some stores have announced extended opening hours for those who have missed Christmas deadlines for online shopping.
Department store John Lewis said it expected trading to be "incredibly busy" this week.
The retailer's director of selling operations, David Barford, said: "This week is always incredibly busy for us but there will also be an element of pent-up demand where shoppers weren't able to get to branches because of the weather.
"It's going to be a very busy week, weather permitting. Customers get to a point where they have to shop."
Individual John Lewis stores had been given the option of making their own decisions to open earlier or close later to make the most of trading conditions, Mr Barford added.
Department store Selfridges said it expected trading to be "busier than
Anne Pitcher, the retailer's buying and merchandising director, said: "Despite the bad weather customers have been shopping in Selfridges in high numbers and we fully expect the last couple of days before Christmas to be busier than ever."
The retailer said it expected more than 250,000 customers to start their festive shopping on Christmas Eve, the majority of them men.
Supermarkets are also expecting tomorrow to be their busiest day ahead of Christmas.
Tesco spokesman Trevor Datson said: "Stores and staff are fully prepared and stocked up ready for our busiest day of the year. We're expecting them to be twice as busy as a normal Saturday. To help cope with the extra demand, thousands of Tesco head office staff have left their desks to help stack shelves, pack customers' bags and serve at the tills.
"The 23rd is the key date for filling baskets with fresh fruit and veg as well as sausages, gammon and stuffing for the Christmas dinner.
Customers also want essentials such as bread and milk so our shelves are topped up with these and other winter warming foods."
Morrisons said it expected 5.15pm tomorrow to be its busiest time of the year.
Spokesman Richard Hodgson said: "After the unprecedented cold weather the UK has had, we know that shoppers won't leave the food shop until Christmas Eve."
Meanwhile, Selfridges announced it was launching its earliest ever Christmas sale, beginning online on December 25.
DIY chain B&Q launched its "January sale" on December 17, promising up to 75% off goods.
Electrical retailer Comet has predicted up to five million people will visit its website and mobile site between Christmas Eve and January 3 ahead of the rise in VAT on January 4 - the highest number the store has seen during the festive period.
It expected a surge of 350,000 bargain hunters going online on Christmas Day, with the majority between 7pm and 8pm, and up to 700,000 visitors on Boxing Day.
Comet spokesman Bob Darke said: "In the run-up to Christmas we've seen a rise in sales of iPads, Kinect for Xbox 360 and 3D TVs, and we expect these to continue to be some of our most popular products.
"With the VAT increase hitting in January 2011, many customers will use the Christmas period to take advantage of deals and snap up some key purchases for the home."