Uber will not be granted a new licence to operate in London, 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 originally lost its licence in 2017 due to safety concerns, but was granted a 15-month extension.
Uber now has 21 days to appeal against TfL’s decision and can continue to operate during that period.
It had received an additional two-month extension in September which expired on Sunday.
Uber has faced resistance from regulators and traditional taxi services in a range of countries after being dogged by controversy for a number of years.
Helen Chapman, Director of Licensing, Regulation and Charging at TfL, 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. 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.”
Fiona Cincotta, market analyst at City Index, told BBC Radio 4’s Today that Uber was likely to appeal.
But she added that if the US firm was unsuccessful: “Here in London, there would be competition that would fill that void quite quickly.”
About 45,000 drivers work for Uber in London, and if its licence is ultimately rejected all of them could lose their jobs.
However, there are other apps providing a similar service which they could join.
TfL can offer licences of up to five years, but it has been more stringent of late.
In July, Indian ride-hailing company Ola got a 15-month agreement for its entry into the London market, while ViaVan got a three-year licence renewal.
In September 2017, TfL said it declined to renew Uber’s licence on the grounds of “public safety and security implications”.
TfL’s concerns included Uber’s approach to carrying out background checks on drivers and reporting serious criminal offences.
Uber’s use of secret software, called “Greyball”, which could be used to block regulators from monitoring the app, was another factor, according to TfL.
At the time, Uber rejected TfL’s claims that it endangered public safety and said Greyball had never been used in the UK for the purposes cited by TfL.