Image caption The Conservatives are warning a Labour victory would turn London into a "laboratory" for Jeremy Corbyn's politics

David Cameron has urged Londoners not to elect Labour's Sadiq Khan as their next mayor, claiming they will become "lab rats" for party leader Jeremy Corbyn's economic experiments.

Speaking at a rally for Tory candidate Zac Goldsmith, the prime minister warned about the dangers of a Labour victory for the capital's economy.

Mr Goldsmith said his Labour rival was "Mr Corbyn's man" in City Hall.

But Mr Khan said he was "no patsy" to Mr Corbyn and would stand up to him.

It is 100 days until London elects a new mayor to succeed Boris Johnson, who is stepping down after eight years.

The vote will be a key electoral test for Jeremy Corbyn and Labour, for whom the capital was one of the few bright spots in last year's dismal general election defeat. Last May, Labour won four seats from the Tories in London and hope to win back City Hall for the first time since 2008.

'Man and the plan'

Addressing a rally of Conservative activists, Mr Cameron sought to frame the election as an early verdict on Jeremy Corbyn's leadership of the Labour party as well as a choice between Mr Goldsmith and Mr Khan.

Image copyright Reuters Image caption Mr Khan has said he will represent all Londoners if he becomes mayor

"Zac Goldsmith can be a great mayor. You've got the man and the plan, think for a moment about the alternative," he said.

"Sadiq Khan nominated Jeremy Corbyn to be leader of the Labour party and he doesn't regret it. Never mind the fact he (Mr Corbyn) wants to give the Falklands back to Argentina or he thinks that nuclear submarines should patrol the Atlantic without any missiles.

"His policy is to bring back and legalise secondary strikes and flying pickets. Just think what the first Corbyn-elected Mayor would be like for our economy, for our city. You do not want to be lab rats in the first Corbyn economic experiment in public life".

Ahead of the rally, the Conservatives launched a poster campaign depicting Mr Goldsmith as "your man in City Hall".

'London's advocate'

In an interview with the Daily Telegraph, Mr Khan said he would stand up to the Labour leader over the issue of Trident renewal and Mr Corbyn's plans for a "Robin Hood" tax on financial transactions, which Mr Khan opposes.

"That is the job of the Mayor of London: not to be a patsy or a spokesperson for George Osborne and David Cameron - as Mr Goldsmith is being - or Jeremy Corbyn or the party, but to be London's advocate to their party and the government."

While he said he did not regret nominating Mr Corbyn for leader - and therefore allowing him to get onto the ballot paper - he said he would have his "own mandate" if he was elected.

"There will be occasions when frankly speaking I disagree with Jeremy," he said, citing his support for Gatwick expansion and pro-business agenda.

He said he wanted to build the broadest electoral alliance: "When you meet and study the best mayors from around the world they are not tribal. What they try and do is to reach across the entire city."

The Liberal Democrats, UKIP, the Green Party and the English Democrats are also fielding candidates in May's election while former Respect MP George Galloway is also standing. The Conservatives and Labour won 84% of the vote between them in the first round in 2012.