Uber will not be granted a new licence to operate in London after repeated safety failures, Transport for London (TfL) has said.
The regulator said the taxi app was not "fit and proper" as a licence holder, despite having made a number of positive changes to its operations.
Uber initially lost its licence in 2017 but was granted two extensions, the most recent of which expires on Monday.
The firm will appeal and can continue to operate during that process.
London is one of Uber's top five markets globally and it has about 45,000 drivers in the city. Overall, there are 126,000 licensed private hire and black cabs in the capital.
If its appeal is unsuccessful, some think Uber drivers would move over to rival ride-sharing firms such as Bolt and Kapten."There would be competition that would fill that void quite quickly," Fiona Cincotta, a market analyst at City Index told the BBC.
Why won't Uber get a new licence?
TfL said it had identified a "pattern of failures" in London that placed passenger safety at risk.
These included a change to Uber's systems which allowed unauthorised drivers to upload their photos to other Uber driver accounts.
It meant there were at least 14,000 fraudulent trips in London in late 2018 and early 2019, TfL said.
The regulator also found dismissed or suspended drivers had been able to create Uber accounts and carry passengers. In one example, a driver was able to continue working for Uber, despite the fact his private hire licence had been revoked after he was cautioned for distributing indecent images of children.
Helen Chapman, director of licensing at TfL, said: "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."
London Mayor Sadiq Khan said: "I know this decision may be unpopular with Uber users, but their safety is the paramount concern. Regulations are there to keep Londoners safe."