Shoppers spend 50 per cent more on Black Friday than on a regular Friday, according to Nationwide figures.
The bank's customers spent £142m on Black Friday 2014, compared to £94.4m normally, and more than half of them bought on a whim. The bank expects the trend to continue this year.
Department stores saw the biggest increase, with Black Friday spending in 2014 up 220 per cent compared to a normal shopping day.
Supermarkets cornered the biggest spend among Nationwide customers, who splashed out £22.56m on Black Friday last, up 24 per cent.
Read more: Black Friday is worth £1.9bn to retailers
But the bank warned that impulse shopping, and fisticuffs, could take over.
In a survey, 51 per cent of shoppers said they'd bought on impulse on the day, and 13 per cent said they'd returned the things they'd bought later. Clear Returns' data suggests over £160m of stock will be returned after Black Friday as buyers have second thoughts about their bargains.
The data also shows one in 10 Brits would be prepared to argue over goods on sale on Black Friday.