The practice of offering bargain basement prices the day after Thanksgiving has spread across the Atlantic, with some retailers opening overnight to lure shoppers.
Police were called early Friday morning to help maintain security at some supermarkets and shopping outlets that offered deep discounts starting at midnight.
Some of the worst problems were in the Manchester area in northwestern England where police were summoned to seven Tesco supermarkets after disturbances.
Greater Manchester Police Chief Peter Fahy said he was "disappointed" that stores did not have enough security personnel on duty for the after-hours shopping.
"This created situations where we had to deal with crushing, disorder and disputes between customers," he said.
Fights broke out at some stores and major websites stopped functioning because of too much traffic as shoppers sought online bargains.
Greater Manchester Police said two arrests were made and injuries reported as police closed some stores to prevent more severe problems. One woman was injured by a falling television set.
The force tweeted "Keep calm, people!" at one point.
There were problems in many parts of Britain, including Wales and Scotland.