Hundreds of thousands of shoppers have flocked to shops across Britain in search of a bargain during the post Christmas Boxing Day sales.

Shopping centers and high streets across London city are packed with shoppers on the traditional Boxing Day sales despite strike action by London's underground train drivers.

Some shops even open as early as 6:00 a.m. (0600 GMT) to attract customers and some shoppers had started queuing outside major shopping centers at midnight.

Up to 7.1 million shoppers are expected to hit the shops on the day, with one in 10 venturing out for a deal before 9:00 a.m. (0900 GMT), according to research from Green Flag.

According to a survey by MoneySupermarket.com, shoppers in Britain are expected to spend a total of 2.9 billion pounds (about 4.7 billion U.S. dollars) on the Boxing Day.

The strike by London tube drivers about bank holiday pay does not seem to have exerted too much impact on the sales, with extra buses were arranged for shoppers to travel to various shopping centers in the city.

Meanwhile, more customers have shifted to online sales on the Boxing Day. Analyst Experian predicted that Christmas this year would be the "biggest and busiest ever" for online retailers in Britain, with visits to retail websites expected to reach 126 million on Wednesday, up 31 percent on 2011 and consumers predicted to spend 472.5 million pounds online.

"Against a tough backdrop for customers and retailers alike, Christmas trading was not exceptional," said Helen Dickinson, new director general of the British Retail Consortium (BRC), in a BRC statement released on Wednesday.

As the post-Christmas sales begin, she highlighted that there's every sign that the ongoing endurance test for retailers of trading in a largely no-growth environment is likely to continue well into 2013.

Dickinson said: "Overall, Christmas hasn't been a boom time for UK retailers but it hasn't been complete doom and gloom either."

"There are big variations in individual retail performances but, when the final sums are done, total spending is likely to be up modestly on last year though only broadly in line with shop price inflation."

"As always, there was a last minute Christmas rush. It came later this year because hard-pressed customers remain cautious, wanted to hold out for bargains and there was a final full shopping weekend immediately before Christmas that the calendar didn't provide last year."

Generally, customers bought only similar amounts to last year. Sales were hard-fought and often driven by discounts so cutting into margins, though retailers worked hard to ensure they had the right products available, whether in store or online, and at the right prices.

"Sales have not collapsed but the pressure is coming from adapting to conditions that consistently deliver minimal year-on-year sales growth. There is only so much cost cutting and new efficiency retailers can achieve," said Dickinson.

She held that utility prices are likely to edge up inflation next year and people are keen to continue paying down their debt, which means the amount of money they have in their pockets will remain under pressure. (1 British pound = 1.62 U.S. dollars)