The Mayor of London Boris Johnson has become the most high-profile Tory in the country to release a video message in support of the global campaign for equal marriage.

Speaking at City Hall, with the Olympic 2012 rings visible on Tower Bridge, he said:

“One of the amazing things about London is that it is not only got a declining crime rate; declining murder rate; more theatres than New York; less rainfall than Rome – but it is also one of the few places in the country where the rate of marriage is actually increasing  –

“And I see absolutely no reason why that happy state should be denied to anybody in our country and that’s why I am supporting the Out4Marriage campaign.”

Mr Johnson initially agreed to follow in the footsteps of Deputy Prime Minister Nick Clegg and fellow Conservative Home Secretary Theresa May in recording an Out4Marriage video after being quizzed by a campaigner at the Talk London debate on 27 June.

However, after several weeks passed without the promised video appearing, Labour Assembly Member Tom Copley formally asked the mayor’s office to explain the delay last week.

In a statement to Pinknews.co.uk, a spokesman for Mr Johnson said: “The Mayor always intended to record a video message, but did not do it as quickly as originally envisaged due to a very busy schedule arising from the London 2012 Games”.

Benjamin Cohen of the Out4Marriage campaign said: “Boris Johnson was one of the first senior Conservative politicians to back the idea of equal marriage, doing so in public before the Prime Minister. He like many has been on a journey when it comes to this issue and we welcome his support for Out4Marriage as we edge closer to the publication of draft legislation to allow gay couples to marry.”

In an editorial praising Mr Johnson’s video, the Evening Standard wrote: “Boris Johnson’s intervention today on the subject of gay marriage throws a lifeline to the Prime Minister on the issue, at a time when Mr Cameron is under fire from many in the Conservative Party. But, more importantly, the Mayor is right on principle to throw his full support behind the reforms.”

Earlier this year, during the London mayoral election race, Mr Johnson was asked if he was surprised by the lengths equal marriage opponents had been going to in their opposition to the UK Government’s plans to allow same-sex couples to marry by 2015.

Mr Johnson told GaydarRadio: “I’m pro marriage, it’s a good thing and I don’t understand the position of those who are so deeply hostile to what is proposed. It seems to me marriage is an ancient human institution and what is proposed is fine.

In 2001, Mr Johnson wrote in ‘Friends, Voters, Countrymen': “If gay marriage was OK – and I was uncertain on the issue – then I saw no reason in principle why a union should not be consecrated between three men, as well as two men, or indeed three men and a dog.”

But in 2010, Mr Johnson became one of the first senior Conservatives to back same-sex marriage, telling PinkNews.co.uk: “If the Conservatives and Liberals [Liberal Democrats] can get together in a national coalition and settle their differences, I don’t see why you can’t have gay marriage.”

Weeks before polling day Mr Johnson had banned two anti-gay Christian organisations from placing homophobic adverts on 26 London buses.

The offensive messages were a direct response to Stonewall’s ‘Get over it!’ bus campaign, aimed to promote gay tolerance and the government’s equal marriage consultation.