Online retailers are expecting bumper internet sales this Christmas with more shoppers than ever logging on to buy iPods and the latest Dan Brown novel.

Visa Europe predicted that today would be the busiest online shopping day of the year with an expected 2.4m online purchases being made using one of its credit or debit cards. On what is now being called Mega Monday, Visa suggested that sales would peak at lunchtime and again at around 7pm when people logged on at home, culminating in a 9% increase on last year's busiest day – 9 December – and a 34% increase on the busiest day in 2007.

For Amazon, last year's busiest day was 8 December when in a 24-hour period it received 1.4m orders, the equivalent of 16 a second. This year it is anticipating even more sales, with the iPod Touch, Joseph Joseph chopping boards and Dan Brown's The Lost Symbol among the most requested items. A spokeswoman said: "We are certainly expecting our busiest Christmas on record."

John Lewis has already beaten its 2008 record for online Christmas sales – on 22 November it sold 48% more than it did on its best-selling day last year – and monthly sales are up between 30% and 40% year-on-year. "Consumer confidence is coming back," according to its head of online selling, Jonathon Brown. "The last few months have been fantastic as customers are shopping for Christmas and we are definitely seeing a surge."

Home Retail Group, the company behind Argos, has already seen huge growth online this year, with figures from data analysts Comscore showing a 25% increase in traffic to its sites. Ross Clenmow, head of multichannel, said it looked set to be "a bumper Christmas".

Smaller shops are also banking on internet sales to see them through the end of the year. Angus McArthur who runs Snow–home, a design store in York, saw online orders double in November.

"Two years ago 10% of our turnover was from online sales. Now it is more like 20%," he said. "For us, there is no single busy day for Christmas orders – it is more like 40 busy days before Christmas."

But while retailers are cashing in, employers are losing out. Research by money saving website VoucherCodes.co.uk estimates businesses are losing £1.4bn a week in lost wages between now and Christmas, with 70% of employees spending time secretly shopping for Christmas gifts instead of working. The research revealed a fifth of workers spend 10 hours out of their working week shopping online.

Figures from IMRG, the industry body for online retailers, show that in the UK internet sales have grown by 14% this year, with shoppers spending just under £40bn in the 10 months to the end of October. Last year UK consumers spent an estimated £9.3bn online during November and December, and this year IMRG expects sales to be 15% higher.

"Despite the recession, the e-retail market is still growing as cash-strapped consumers look to the internet to find the best possible deals," the group's director of information, Tina Spooner, said. "I think online retailers can look forward to a very merry Christmas."

According to IMRG, the strongest performing sectors since the start of this year have been clothing and electricals, where despite taking a hit during the postal strikes sales are up by 18% and 20% respectively. Figures from Comscore put book retailers at the top of the tree, receiving 18m visitors to their sites in October, 38% up on the same period last year. Clothing retailers are next with 16m visitors during the month, a rise of 11% on October last year.