Recent years have seen online shopping figures consistently peaking on the first Monday in December, probably because many UK consumers have received their last pay cheque before Christmas.
Visa Europe predicts £320 million will be spent on its cards alone as online transactions top 6.8 million, an increase of 21% on last year, making December 3 this year the busiest online shopping day in history.
This month will also see more than £11 billion withdrawn from cash machines, equating to more than £41,000 per second in the pre-Christmas peak.
Sainsbury's Bank predicts a 1.3% rise in cash withdrawals compared with December last year to reach a total of £11.1bn, due to an increased number of ATMs across the country, resulting in increased accessibility.
Visa Europe commercial director Dr Steve Perry said: "On Mega Monday, people across the UK will go online and use their Visa cards to make 6.8 million transactions, the most in a single day in UK history. That's 21% more than in 2011, signalling that consumers are becoming increasingly accustomed to the advantages of shopping online."