Springboard said Covid was a "key reason" for a bounce back from 2021 when the Omicron variant was spreading and some restrictions were in place.

The firm added that good weather in some areas tempted shoppers out.

But numbers are still sharply below 2019 and people are expected to spend less due to the higher cost of living.

Footfall is down more than 30% compared to Boxing Day three years ago before Covid struck.

Springboard added that figures this year may have been helped by the fact that Boxing Day last year fell on a Sunday when many stores decided to stay closed or had reduced trading hours.

Diane Wehrle, insights director at retail analyst Springboard, told the BBC the data was "encouraging" for retailers, but that rising living costs are clearly having an impact.

The drop versus Boxing Day 2019 is "attached obviously to the cost of living crisis," she added.

"People are dealing with that, so a lot of people may rail back on going out on Boxing Day and spending money they perhaps don't need to spend."

Ms Wehrle added 27 December could turn out to be a more important date for retailers than the 26th.

"While some stores may not be open today, they will reopen on the 27th and that's an important trading day, and perhaps that is actually starting to grow in importance," she said.

Springboard said that despite the rail strike on Monday, footfall in central London - which has been the hardest hit of any location due to travel disruption - showed the sharpest increase in footfall for any area across the UK.

It rose by more than 139% compared to 26 December last year.

However, separate research suggests that shoppers may be intending to spend less this year.

Barclaycard predicts that the average person is set to spend £229 in the post-Christmas sales, £18 less than last year.

In a survey of 2,000 would-be shoppers, the credit card firm by Barclaycard found that 42% said the higher cost of living would temper spending in the post-Christmas sales, with many of those saying they would spend less compared to previous years.

The rate of price rises - also known as inflation - hit 10.7% in November which was lower than October but is still at its highest for 40 years.

Dr Sarah Montano, retail expert and senior lecturer of marketing at the University of Birmingham, said: "For many consumers, obviously they would've been shopping pre-Christmas, as we had the Black Friday sales and things like that.

"As we move into the new year, we expect consumers to be a bit cautious because of course, the heating bills will still be to come for consumers and that will impact on their discretionary spending."

Harshna Cayley, head of online payments at Barclaycard Payments, said: "The rising cost of living and inflationary pressures have naturally had an impact on the amount being spent in the post-Christmas sales this year.

"Having said that, retailers can take confidence knowing that shoppers still plan to make the most of the deals and discounts on offer."

Mike Ranson, general manager at Tessuti, a clothing store in Liverpool, told the BBC that Boxing Day remained "one of the most important days of the year for us".

But he said that the store has introduced steep discounts across its goods. "We are doing up to 50% across all brands, so we've got discounts across I'd say 90% of the brands across the stores. We have gone pretty big on sales this year."

Many people, especially teenagers and young adults, will have received cash or gift vouchers and may look to spend them in the Boxing Day sales.

"Retailers will be wanting to attract them and get a nice boost post Christmas," said Dr Montano

Rail strike

Meanwhile, rail firms have warned that services could be disrupted for much of the coming week. Network Rail workers who are members of the RMT union are holding strike action until 06:00 GMT on 27 December.

Industrial action on the railways could mean that roads are busier than usual, with shoppers facing traffic as they head out to the sales.

Football fans are also expected to have taken to the roads on Monday, due to the rail strikes.

The AA forecasts that 15.2 million cars will have been on the roads during the day.

A spokesman for the motoring group said delays started building from mid-morning, adding that by midday there had been "some serious delays on the M25 and the M6".