"Despite addressing some of these issues, TfL does not have confidence that similar issues will not reoccur in the future, which has led it to conclude that the company is not fit and proper at this time."
It claimed the company allowed unauthorized drivers to upload their photos to other Uber driver accounts, allowing them to pick up passengers as though they were the booked driver — which occurred in at least 14,000 trips.
"This means all the journeys were uninsured," it claimed, adding that some passengers were obliviously being driven by drivers who had had their licenses revoked.
Another failure allowed dismissed or suspended drivers to create an Uber account and carry passengers, again compromising passenger safety and security, it said.
"As the regulator of private hire services in London we are required to make a decision today on whether Uber is fit and proper to hold a licence," said Helen Chapman, Director of Licensing, Regulation and Charging at TfL.
"Safety is our absolute top priority. While we recognise Uber has made improvements, it is unacceptable that Uber has allowed passengers to get into minicabs with drivers who are potentially unlicensed and uninsured."
The ride-share firm now has 21 days to appeal, during which it can continue to operate, before driving for the company becomes illegal.
The firm, which is used by approximately 3.5million people in the UK capital, said it indeed plans to appeal.
This is the second time Uber has lost its license to operate in London since it began operating there in 2012.
In 2017 the TfL moved to suspended its license over safety issues, including flawed background checking methods. A judge overturned this decision and granted it a 15-month temporary license on the promise to address the concerns; this was then extended for a further two months in September by TfL.