US ride-hailing giant Uber on Monday won an appeal to operate in London after a judge ruled it was a "fit and proper" firm despite safety concerns.

Uber -- which has 3.5 million customers and 45,000 drivers in the British capital -- overturned Transport for London's (TfL) refusal last year to renew its operating licence around the issue of unauthorised drivers.

The San Francisco-based company was permitted to continue operating in London during the appeal process.

"Despite their historical failings, I find them, now, to be a fit and proper person to hold a London PHV (private hire vehicle) operator's licence," said deputy chief magistrate Tan Ikram, sitting at a central London court.

He noted that Uber had sought to explain how breaches had taken place and how they would be remedied.

The judge did not state the length of the licence -- but Uber said in a separate statement that it would be for 18 months and welcomed the ruling.

"This decision is a recognition of Uber's commitment to safety and we will continue to work constructively with TfL," said Jamie Heywood, regional general manager for northern and eastern Europe.

"There is nothing more important than the safety of the people who use the Uber app as we work together to keep London moving."

Heywood admitted that Uber's behaviour over the problem of unauthorised drivers had been wrong.

"It was not what we would do now. It was inadequate, we could have done better," he said.

TfL, chaired by Mayor of London Sadiq Khan, has yet to give an official response.

In November last year, the transport authority argued there was a "pattern of failures" at Uber in the capital.

Some trips took place with unlicensed, suspended or dismissed drivers, according to the authority. Ikram on Monday said the company appeared to be addressing those concerns.

He acknowledged that Uber had tightened up its review processes in relation to issues of document and insurance fraud.

"Uber does not have a perfect record but it has been an improving picture," Ikram said. "The test as to whether Uber are a 'fit and proper person' does not require perfection. I am satisfied that they are doing what a reasonable business in their sector could be expected to do, perhaps even more," he added.

Uber's London operation has suffered previous licence suspensions in addition to protests from the capital's traditional black cab drivers.