Springboard, which analyses customer activity in stores, said footfall up until midday had seen the largest decline since 2010, dropping by 10.6%.

It said Boxing Day was becoming less important as a trading day.

But there were still queues for some shops from as early as 04:30 GMT.

The footfall figures were the largest decline of any year since data was first published by Springboard 10 years ago. The retail data analyst examines information from UK High Street and shopping centre cameras.

Diane Wehrle, insights director at Springboard, said the final figures might improve but they are still likely to be substantially down on last year.

She said many consumers were still celebrating Christmas with their family on Boxing Day, while the rainy weather, online shopping and increased Black Friday spending were also possible factors for the drop in footfall.

"Boxing Day is indisputably a less important trading day than it once was," Ms Wehrle said.

Some bargain-hunters did brave the rain, with some shoppers on London's Oxford Street waiting for stores to open at 9am.

Others queued outside Selfridges in Greater Manchester's Trafford Centre at 4.30am.

As the doors to Next opened in Liverpool at 06:00 GMT, more than 150 people were waiting outside the store.

A total of £3.7 billion was expected to be spent in the Boxing Day sales, according to Barclaycard, with four in 10 UK adults predicted to spend an average of £186 each.

But environmental concerns were also expected to drive down buying, with shoppers also predicted to spend £200 million less in post-Christmas sales this year compared to last year.

Opinium Research surveyed 2,002 UK adults online for Barclaycard between 29 November and 3 December.