Uber has been stripped of its license to operate in London, as the local transport regulator said it was "not fit and proper."

Transport for London said Monday that it would not renew the San Francisco-based ride-hailing giant operator's license, citing a "pattern of failures" that had "placed passenger safety and security at risk."

TfL had first suspended Uber's license back in 2017, flagging concerns with the company's approach to safety. Following that initial move, Uber had twice been granted a temporary license to continue operating in the city — the first, a 15-month reprieve issued by a judge last year, and the second, a two-month permit granted by TfL in September.

"Uber has made a number of positive changes and improvements to its culture, leadership and systems in the period since the Chief Magistrate granted it a licence in June 2018," TfL said in a statement Monday. "This includes interacting with TfL in a transparent and productive manner."

"However, TfL has identified a pattern of failures by the company including several breaches that placed passengers and their safety at risk," the regulator continued. "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."

Uber now has 21 days to appeal the decision and will be allowed to operate during that time. In response to TfL's move, the company said it intended to appeal.

"TfL's decision not to renew Uber's licence in London is extraordinary and wrong, and we will appeal," Jamie Heywood, Uber's regional general manager for Northern and Eastern Europe, said in a statement. "We have fundamentally changed our business over the last two years and are setting the standard on safety. TfL found us to be a fit and proper operator just two months ago, and we continue to go above and beyond."

"On behalf of the 3.5 million riders and 45,000 licensed drivers who depend on Uber in London, we will continue to operate as normal and will do everything we can to work with TfL to resolve this situation."

London is Uber's biggest European market and a key driver of its revenues beyond the U.S. It's faced increased competition in the U.K. capital from the likes of Estonian start-up Bolt and French rival Kapten.

In its announcement, London's transport authority said it held issue with a change made to Uber's systems that allowed unauthorized drivers to upload their photos to other Uber driver accounts. According to TfL, this allowed them to pick up riders as though they were the booked driver.

"This means all the journeys were uninsured and some passenger journeys took place with unlicensed drivers, one of which had previously had their licence revoked by TfL," the regulator said.

This is a breaking news story. Please check back for more updates.