Shoppers are expected to have spent £150m this weekend in the West End alone.
And retailers expect to take up to £300m before Christmas, according to the New West End Company.
Footfall has also risen by 6.7 % from 2013, it said.
Tuesday between 1-2 pm is set to be the busiest hour on the busiest shopping day across Britain, according to the credit card provider Visa.
Shoppers have battled crowds across central London in the hunt for late Christmas bargains on a day when £1.2 billion was expected to be spent on Britain's high streets.
Sales on Bond Street, Oxford Street and Regent Street alone was tipped to surpass £150 million during the vast consumer spend, which has been branded "Panic Saturday".
Londoners are expected to spend around £150 million this weekend beginning on 'panic Saturday' as shopping days before Christmas dwindle.
The New West End Company predicted the retail takings, and said that footfall in the West End this morning was up 7.1% year on year.
Britons save an average of £742 a year using rewards points and vouchers, but Londoners are less savvy with shopping deals. A survey for American Express has found shoppers in Scotland save the most, £1,019 a year through special deals and vouchers. But in London the average saving is £708.
London shoppers were out in force yesterday to bag a Boxing Day bargain.
The number of people who visited stores in London for the Boxing Day sales was up 10.5% from last year.
In the West End alone, the number of shoppers increased by 11.8%.
West End sales were expected to each more than £50 million, but the official figures are yet to be released.
Stores in the capital are braced for chaos today as the Boxing Day sales begin.
Harrods is expecting so many shoppers to turn up that it is providing hot chocolate and entertainment outside to queueing customers from 9am, an hour before it opens its doors. In previous years shoppers have queued from 5am to try and get their hands on cut price designer goods.
The West End is expected to be one of the busiest shopping destinations in the country - with around 800,000 shoppers hitting the area on Boxing Day last year.
The West End is set to see an influx of shoppers eager to do some last minute shopping today.
Last year around 400,000 customers hit the area's shops in the last few days before Christmas, but businesses expect more this year due to the weekend's poor weather.
Tens of thousands of people descended on the capital's shops today for what was expected to be one of the busiest and most stressful days in the run-up to Christmas
But as big name stores slash prices to make us spend, one debt charity warns that it won't be a Merry Christmas for everyone.
ITV London's Ruth Banks reports from Oxford Street:
Overseas tourists have helped shops in central London see an estimated spend of £380 million. Retailers in Bond Street, Regent Street and Oxford Street also saw a 6.7 per cent increase in their footfall over the recent half-term period.
The average spend for visitors from the Middle East and Russia was £1600 and £603 respectively.