Zac Goldsmith has lost the race to become London Mayor as his Labour rival Sadiq Khan defeated him by more than 300,000 votes

Mr Khan was ahead in the polls throughout the campaign, and early indications today put him ahead by 9 per cent.

The Tooting MP won the keys to City Hall with 1,310,143 votes to Zac Goldsmith's 994,614.

Mr Goldsmith’s attention will now return to his Richmond Park and North Kingston constituency and David Cameron’s upcoming decision on whether to expand Heathrow.

In his speech, Mr Goldsmith said: "I'm disappointed of course by the result, that I won't be able to deliver a manifesto that I'm really proud of.

"I planned to make London the cleanest and greenest city in the world.

"I want to pay tribute to all my fellow candidates and in particular Sadiq Khan.

"I wish him well as he sets out to build on the successes that we have seen from Boris Johnson."

The Conservative, an MP since 2010, said he would resign if David Cameron gave the go-ahead for a third runway – a move he later said he regretted.

He previously said it would be an ‘act of betrayal’ if Mr Cameron approved the plans.

The announcement was made shortly after 12am after "small discrepancies within the electoral figures" caused a severe delay as officials checked the results.

Mr Goldsmith has been criticised for running a negative campaign, calling into question the Mr Khan for sharing platforms with those he described as ‘extremists’.

He criticised the Tooting MP for appearing at events alongside figures such as Babar Ahmad and Suliman Gani.

In his victory speech, Mr Khan said: "London is the greatest city in the world. I am so proud of our city. I am deeply humbled by the hope and trust you have placed in me today.

"I'm so proud that London has chosen hope over fear, and unity over division. I hope that we will never be offered such a stark choice again.

"I promise to always be a mayor for all Londoners, to work had and make life better for every Londoner, despite your background."

Mr Khan will take over from Boris Johnson as Mayor after eight years at the helm, with the housing crisis and freezing fares across Transport for London his top priorities.