Conservative London Mayor candidate Zac Goldsmith has said housing “will define the next mayoralty” and has pledged to build 50,000 homes a year in the capital.

The MP for Richmond Park, in south-west London, called this his “top priority” and said he wants to “grow the transport network to enable us to solve the house crisis”.

The 41-year-old son of billionaire financier Sir James Goldsmith is the main rival to Labour’s Sadiq Khan in May’s election.

He told the Recorder: “I want to protect and build on what Boris has done, I think he has been a really successful Mayor, but that has come at a cost.

“People are being priced out of their own city. You could be on an average wage and you would struggle to buy your own home.”

Mr Goldsmith believes supply is key and has promised to build 50,000 homes a year while in office.

“Capital is not the issue, look at the investment waiting to go into local authorities,” he said.

“The political obstacle is the land and I would work with Transport for London to unlock brownfield sites and lobby the government to release that.”

He promised any homes built on mayoral land will only be sold to Londoners – people who have lived or worked in the capital for three years and do not own a home.

He assured voters there would be affordable options “due to increasing supply, with shared ownership, help-to-buy and starter homes”.

The Tory candidate, a keen environmentalist who grew up idolising David Attenborough, pledged to protect Newham’s green belt.

He has said he would resign his seat and trigger a by-election if Heathrow built a third runway.

“The environment is now a deep concern for people, not just protecting our green spaces, but improving air quality as pollution claims millions of lives,” he said.

Mr Goldsmith added that he would work to improve both the physical and mental health of Londoners.

“The Mayor has got a big public health brief,” he said.

“One of the big issues is to protect our green spaces and also deal with air quality.

“We have all the tools to clean up our air, I think we can solve that problem pretty quickly.

“A big remit relates to mental health. It comes into all parts of life.

“If we tackle that it will take some pressure off police time as well. I will work with the government provide a better strategy for mental health.”

Much has been made of the £200million fortune Mr Goldsmith inherited, but he disagreed that Mr Khan, the son of a London bus driver, would be more relatable and electable for Newham’s residents.

He said: “How would this be one of the most diverse cities on earth if you just elect a candidate who looks like you, you aren’t going to do that. I don’t think people make huge decisions like that, the same way they don’t make them based on politicians’ promises.”