John Lewis and Marks & Spencer have fired the starting gun on the Boxing Day sales as figures suggest Britons will spend £1.1bn shopping online on Christmas Day.

After a difficult year, the department store chain has begun a clearance sale on its website with the biggest reductions in its homewares departments. M&S has launched what is describes as its “biggest sale of the year”, with deals of 50% off in its clothing and homewares departments.

The shops may be closed but nearly 11 million Britons will still go shopping online on Christmas Day, spending just over £100 on average, according to research by the Centre of Retail Research (CRR) for the website VoucherCodes.co.uk. The size of the virtual shopping spree on 25 December has risen from £728m in 2015 to a predicted £1.1bn in 2018.

“A lot of retailers will launch their Boxing Day sales on Christmas Day or even Christmas Eve so … a bit of online bargain hunting might just beat some of the TV Christmas specials,” said Anita Naik, of VoucherCodes.

A tough year for the high street has ended with a difficult Christmas. Retailers have cut prices after consumer confidence hit a five-year low during the biggest shopping weeks of the year.

Currys PC World’s sale will also start on Christmas Eve night.

The squeeze on living standards means Britons are more eager than ever to save money in the sales, with the CRR predicting £4.75bn will be spent in stores and online on Boxing Day. They predict nearly 18 million people will visit their local high street or shopping centre on Wednesday.

A separate shopper poll by Barclaycard found four in 10 adults plan to shop in the sales, spending an average of £188 each. Men will be the biggest spenders, shelling out 50% more than women at £227 compared with £151.

There was also evidence that bargain-hunters planned to start their sales shopping even earlier the usual, with three in 10 beginning their spree on Christmas Eve and 17% on Christmas Day.

“Boxing Day remains the most popular day to shop for bargains over the Christmas period,” said Konrad Kelling, managing director of customer solutions at Barclaycard. “However, this year the majority of consumers plan to shop online from the comfort and convenience of their own home rather than braving the winter weather and crowds on the high street.”

On Christmas Eve the high street was already a sea of red sale signs with Debenhams, House of Fraser, Topshop and New Look among the fashion brands offering up to 70% off deals. The desperate price cutting came after stores were not as busy as expected on the biggest shopping day of the year.

“It was called Super Saturday but it was not particularly super,” said Diane Wehrle, Springboard’s marketing and insights director. “Footfall on Friday and Saturday was lower than last year, by 6.5% and 0.7% respectively.”

The scale of discounts now on offer appeared to draw shoppers to the high street on Christmas Eve with Springboard reporting footfall up nearly 7% on last year by lunchtime. For shopping centres the figure was nearly 10%.

“Shoppers appear to have changed their pattern of shopping, leaving it almost to the very last opportunity to visit retail destinations,” said Wehrle. “Part of this is likely to be the opportunity to take advantage of additional discounts introduced by retailers today in order to clear as much stock as possible.”

Earlier this month the Sports Direct boss, Mike Ashley, said Debenhams and other big retail names faced being “smashed to pieces” by a savage high street downturn. The tough conditions have already resulted in some large casualties. The fashion website Asos and Superdry were among the chains to issue severe profit warnings in the run-up to Christmas.

In some rare good news for the high street it emerged that the Hull branch of House of Fraser had been granted a reprieve. Sports Direct bought the collapsed chain out of administration in August and has since been in the process of renegotiating rental agreements with landlords.

The Hull store, known locally as Hammonds, was to shut on Saturday but the company said it had struck a deal with the landlord and Hull city council.