The London mayor is seeking powers to limit the number of private hire drivers operating in the capital city of the United Kingdom.

As the rise of Uber and its competitors is blamed for increasing congestion and pollution, Sadiq Khan said a cap on new licenses was an urgent and necessary step, but added that he is unable to impose restrictions.

The mayor has warned Transport Secretary Chris Grayling that the "huge increase" in private hire drivers in the city is leaving many drivers struggling to earn a living.

The Department for Transport is considering the proposal.

But the Licensed Private Hire Car Association (known as LPHCA) said a cap would only push up prices, make it harder for companies to recruit drivers and leave minicab users stranded.

Last week, New York became the first major US city to approve a cap on ride-hail car licenses－which includes app-based services such as Uber.

In a letter to Grayling, Khan said: "Unlike New York, I don't have the power to cap the number of private hire vehicles in London. I am writing to again urge the government to grant me that power as the mayor of London－alongside appropriate restrictions on cross-border hiring, to enable Londoners, like New Yorkers, to breathe better air and live in a less congested city."

The New York decision, Khan said, showed it was something that "can definitely be done".

In 2010-11, Transport for London counted 61,200 private hire drivers and 50,663 private hire licensed vehicles in London. This went up to 113,645 drivers and 87,921 vehicles in 2017-18－an increase Khan described as "massive" and "unsustainable".

But Steve Wright, chairman of the LPHCA, said: "This is a ridiculous proposal. It's just a draconian thing from years gone by. It's protecting the black cab industry and will be detrimental to consumers."

Uber recently won a 15-month license to continue operating in London while its Indian rival Ola this month announced plans to expand into the UK.

An Uber spokesman said: "Uber is committed to helping address congestion and air pollution and we strongly support the mayor's ultra low emission zone.

"Already more than half of the miles traveled with Uber are in hybrid or electric vehicles.

"By getting more people into fewer vehicles and investing in our clean air plan, we can be a part of the solution in London."