Retailers are predicting that today will be the biggest online shopping day of the year as consumers ramp up their Christmas spending.

Visa, which labelled the annual shopping event ‘Mega Monday’, is expecting £303m to be spent online in the UK using its cards.

This equates to £3,500 per second, a 12% increase on 2010.

Visa says the Monday closest to the beginning of December is historically the busiest day for online shopping as pay day for a majority of consumers falls on the last Friday of the month, who then spend the weekend browsing shops before buying online on the subsequent Monday.

The IMRG, the industry body for online retailers, says that today is the start of two weeks of peak activity.

It predicts that £3.72bn will be spent online over the next two weeks, a 14% increase on last year.

However, Amazon says next Monday will actually be its busiest shopping day, as traditionally shoppers head online on the first Monday in December.

The online retail giant said it received 2.3m orders on Monday 6 December last year.

And to add to the confusion, Joshua Bamfield, director of the Centre for Retail Research (CRR), says that ‘Cyber Monday’ is an American phenomenon and he expects to see two peaks in online shopping.

One of the peaks occurred on Monday 21 November and the other is set to occur this Sunday. According to Barnfield:

You get a peak in November with the organised people who want to do things early and make sure the toys and gifts get delivered in good time, then there will be those who turn the calendar over this week and realise that it’s suddenly December and they start panicking causing another peak.

The CRR predicts that £13.4bn will be spent online in the build up to Christmas, a 16.3% increase on 2010.

Of the total online spend, the CRR says that £1.64bn will be spent on mobiles.

Regardless of which day proves to be the busiest, all the predictions suggest that this will be the busiest festive period yet for online retailers.

Statistics we compiled after last Christmas show that spending is up year on year, with John Lewis reporting a 42% increase from 2009 to 2010.

And with one in ten Brits stating they will do their Christmas shopping using a mobile, campaigns such as House of Fraser’s tie up with O2 are an important tool in the battle for our ever-increasing online Christmas spend.