Shoppers spent £968 million online on Monday alone, or £672,000 a minute - 34% more than the £720 million spent last year, figures from Experian-IMRG show.
However the amount is less than for Black Friday when shoppers shunned the high street to spend £1.1 billion online, or £763,000 every minute.%VIRTUAL-ArticleSidebar-black-friday%
Experian Marketing Services senior retail consultant James Miller said the figures showed consumers had fully embraced the online shopping "phenomenon".
He said: "Retailers still have more opportunities to reach customers in the run up to Christmas, with Manic Monday on December 7 representing the time when consumers look to order gifts to ensure they receive them before Christmas, before the traditional Boxing Day sales begin."
Amazon.co.uk said yesterday was its busiest Cyber Monday, with orders peaking at 9.36 pm, but Black Friday was its biggest sales day ever, when customers ordered more than 7.4 million items at a rate of around 86 items per second.
Amazon.co.uk managing director Christopher North said: "Cyber Monday remains one of our biggest days and continues to grow every year but its position as the biggest day in the online retail calendar has now been taken by Black Friday.
"We expect to see high demand from customers continue from this point forward with increasing numbers shopping right up until Christmas Eve as a result of superfast delivery options."
Experian-IMRG predicts consumers will spend another £733 million on Manic Monday, up 10% on last year, followed by £728 million on Christmas Day, £856 million on Boxing Day and £638 million on New Year's Day.
This year's Black Friday bonanza was the first time in the UK that online retail sales surpassed £1 billion in one day.
Black Friday was the Tesco Direct website's busiest ever 24 hours online and Currys PC World's website had over 6.5 million visitors between Friday and Sunday.
Cyber Monday marks the end of a four-day pre-Christmas shopping splurge over the Thanksgiving holiday in the US but it has become a busy online shopping day in the UK thanks to discounting by retailers.