LONDON (REUTERS, NYTIMES) - More than half a million people have signed a petition calling for London's transport authorities to reverse their decision to strip the licence of ride-sharing firm Uber.

The "Save Your Uber" campaign in London was set up by Uber on the Change.org website after it was announced on Friday (Sept 22) that the firm's licence will not be renewed when it expires on Sept 30.

Transport for London (TfL) said the Silicon Valley technology giant's approach and conduct was not fit and proper to hold a private vehicle hire licence. The British regulator said it would let Uber operate until the appeals process is exhausted, which could take months.

"Uber's approach and conduct demonstrate a lack of corporate responsibility in relation to a number of issues which have potential public safety and security implications," TfL said.

Specifically, TfL cited Uber's approach to reporting serious criminal offences, background checks on drivers and software called Greyball that could be used to block regulators from gaining full access to the app.

The TfL decision was backed by London mayor Sadiq Khan and the capital's thousands of black cab drivers.

A ban on operating in one of its largest markets would hit Uber's bottom line. The company said it had 40,000 drivers and 3.5 million customers in London who used its app at least once every three months.

In a break with the startup's usual combative tone, Uber's new Chief Executive Dara Khosrowshahi asked London to work with the ride service.

He wrote in a tweet: "Dear London: we r far from perfect but we have 40k licensed drivers and 3.5mm Londoners depending on us. Pls work w/us to make things right."

In an e-mail to Uber employees, Mr Khosrowshahi said he thought the London decision was unfair, but "the truth is that there is a high cost to a bad reputation."

He added that "it's critical that we act with integrity in everything we do, and learn how to be a better partner to every city we operate in."

Mr Khosrowshahi was brought in to steer the company after a string of scandals involving allegations of sexism and bullying.

Uber London General Manager Tom Elvidge made a combative response, saying the London mayor and regulators had "caved in" to people who want to restrict consumer choice. He added that Uber would "immediately challenge" the decision in court.

The loss of the licence in London comes after a tumultuous few months that led to former CEO and co-founder Travis Kalanick being forced out. Uber, which is valued at about US$70 billion (S$94 billion) and whose investors include Goldman Sachs, has faced protests around the world for shaking up long-established taxi markets.

The taxi app has also been forced to quit several countries, including Denmark and Hungary, and faced regulatory battles in multiple US states and around the world.

Uber debuted in London in 2012, just before the Summer Olympics, initially with a luxury service. It added UberX, which competes more directly with the city's storied black cabs, a year later. The company now operates in more than 40 cities and towns across Britain.

Its arrival in London, however, created a clash almost immediately with the black cabs, which trace their roots to 1634. Black-cab drivers, who earn their licences by memorising some 25,000 streets and 100,000 landmarks for a famously exacting test known as The Knowledge, complain that Uber drivers are under-regulated.

Many fear that the rivalry will put them out of business: Uber fares are about 30 per cent lower than those of black cabs.