London Mayor Sadiq Khan has urged Theresa May to give the go-ahead for a second runway at Gatwick as quickly as possible.

He described it as "one of the first major tests for the new Prime Minister" and claimed expanding Gatwick instead of Heathrow was the "better option for London".

Heathrow responded by saying there were significantly greater benefits to its proposal to build a third runway.

In a speech at Gatwick, Mr Khan said: "There's now one obvious choice for Theresa May to take: a second runway here at Gatwick."

The whole of the UK would benefit from the economic boost created by increasing capacity at Gatwick and new opportunities for growth would be generated, particularly in south London, the mayor said.

He told the audience of airport employees that a second runway would lead to greater competition which would increase standards, choice and efficiency while lowering prices for passengers.

"Crucially, this choice would mean we can meet the future aviation capacity requirements of London and the South East whilst keeping our air quality safe and within legal limits," he said.

"I'm calling on our new Prime Minister to make the right choice and to make it quickly.

"Gatwick is not only the faster and cheaper option, but the cleaner and better option for London."

Mr Khan made his speech as Gatwick announced an additional £200 million investment in the existing airport to expand its North and South terminals, upgrade shopping facilities and create larger immigration halls.

The Airports Commission recommended in July last year that a third runway at Heathrow should be built.

But in December the Department for Transport announced that further investigation into noise, pollution and compensation was needed, and last month said the decision had been deferred until ''at least October'' following David Cameron's resignation as prime minister.

A Heathrow spokesman said: "The Airports Commission disagree with Sadiq Khan and Gatwick.

"Following an independent, £20 million, two-and-a-half-year deep-dive into the issue of airport capacity, they confirmed that Heathrow expansion could provide the capacity the UK needs more easily and quickly than any other option.

"Brexit makes the Commission's conclusion that, with Heathrow expansion, 'the benefits are significantly greater, for business passengers, freight operators and the broader economy', even more persuasive."