London's transportation authority announced on Monday that Uber would no longer be allowed to operate in the city after "a pattern of failures" by the company that placed passengers' safety at risk.
Transport for London identified that a change to the company's system had been allowing unauthorized drivers to use accounts belonging to other Uber drivers.
"This allowed them to pick up passengers as though they were the booked driver, which occurred in at least 14,000 trips, putting passenger safety and security at risk," the transport authority said in a statement.
This means all those trips were uninsured. Some took place with unlicensed drivers.
Uber said it would operate "as normal" in London while it appealed the decision.