Taxi app Uber lost a court battle on Friday to stop a London regulator from forcing private hire drivers to prove their reading and writing skills in English, the latest setback for the firm in London which could now lose some workers.

San Francisco-based Uber, which allows users to book journeys at the touch of a button on their smartphone, has faced bans and protests around the world as regulators play catch-up with technology disrupting traditional operators.

Uber launched legal action in August after public body Transport for London (TfL) said that drivers should have to prove their ability to communicate in English, including to a standard of reading and writing which Uber said was too high.

"TfL are entitled to require private hire drivers to demonstrate English language compliance," said Judge John Mitting as he rejected Uber's claim.

Uber said earlier this week in court that having such a high level of required English competence could mean about 33,000 London private hire drivers lose their licenses.

The decision is the latest setback to the firm in Britain after a tribunal ruled in October it should treat its drivers as workers and pay them the minimum wage and holiday pay, a verdict the firm is appealing.

The firm, however, did manage to overturn proposals by TfL on Friday for drivers to have permanent private hire insurance and for Uber to operate a 24/7 call center.