Ride-sharing firm Uber has lost its license to operate in London, in part due to an issue that led to unauthorised drivers picking up passengers.

Transport for London (TfL) says the the Silicon Valley-based is not "fit and proper to hold a private hire company in the capital" because of a "pattern of failures" that places passenger safety and security.

TfL says it identified a major security issue where unauthorised drivers were able to upload their photos to other driver's Uber accounts. The transport regulator says this resulted in over 14,000 trips.

In a press release on Monday, Transport for London wrote: "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 also says the company enabled fired or suspended drivers to create accounts.

Uber now has 21 days to respond to the ruling, during which it can continue to operate. During that process, Uber can attempt to demonstrate that it has put "sufficient measures" to ensure the safety and security of passengers.

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.

"It is clearly concerning that these issues arose, but it is also concerning that we cannot be confident that similar issues won't happen again in future."

In a statement, Uber says: "We think this decision is wrong and we will appeal."

It added: "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."