There are those who point to Labour’s performance in London as a rare success at the general election. It is an understandable reaction - looking for a glimmer of optimism in the context of a disastrous election result. Unfortunately, though, it is wrong. Yes, the tireless work of our activists meant we gained four new seats and four great new MPs. But we won fewer than half the seats we were expecting to gain from the Tories. Our vote share went up, but only to 44 per cent - well short of the margin needed to win next years’ mayoral election. Since 2005, we have made a net gain of just one seat in London. And, of course, we’ve lost the last two mayoral elections to the Conservatives.

Despite an incredible number of hard-working activists, the messages and policies coming out of party HQ just didn’t resonate with millions of Londoners in seats like Harrow East, Finchley & Golders Green, Croydon Central and Battersea. It is the support of exactly these voters that Labour needs if we are to win the mayoralty next year and deliver the London seats we need if we are to put a Labour Prime Minister in Downing Street in 2020. It is now more important than ever that we choose a mayoral candidate who can broaden our appeal. That candidate needs to be someone who will lead from the front, who has the ability to reach beyond party lines and inspire Londoners from all backgrounds.

That’s why I’ve decided to support David Lammy to be the Labour candidate for mayor. In fact, I’m very pleased to be chairing his campaign. The other candidates all have their strengths, but they represent an old style of politics that has proven to fail in London. The importance of winning in the capital means this isn’t the time for party insiders or tribal and divise figures. We need new leadership in London and David is best placed to provide that.

David gets London. He’s seen every side of the city, from growing up in the shadows of a council estate in Tottenham and working in KFC to help support his single mum, to becoming a barrister and a government minister.

But a good back story isn’t enough – Londoners want to look forward, not back. The next Mayor needs to have a vision for London. With his campaigns and policy proposals, David has made clear that he has that vision. He’s published by far the most bold, sensible and far-reaching proposals on housing of any mayoral candidate. He says what he thinks, stands up to vested interests and is a tireless campaigner on a range of issues, from fighting the spread of betting shops to being the first to call for rent controls to standing up for fathers. He’s got Labour values at his core but is also an independent thinker and an authoritative voice. He speaks with authenticity on the issues that matter to Londoners in a way that no other candidate is able to do.

To win over the swing voters who, because of the voting system, are needed to win the mayoralty, our candidate has to be someone who can reach beyond narrow party lines to deliver the capital for Labour. They need to be able to stand up for vested interests rather than being in their pockets. David is forward-looking and inclusive. He’s not a tribal figure – I’ve seen him in action with constituents in Tottenham and speaking to business leaders, and he was able to connect equally impressively with both.

David is a normal Londoner, whose story exemplifies all that is good about our city. He’s passionate about the challenges the city faces about but optimistic and determined about our ability to overcome them. He’s a proven leader who always stands up for those who need it. While other candidates boast of their experience fighting marginal seats, David has had far bigger challenges to deal with: who could have failed to be impressed by the passion and leadership he showed after the 2011 riots in Tottenham? He was out on the streets reducing tensions while castigating rioters for destroying their own neighbourhoods. At the same time, he brilliantly articulated the alienation that so many young Londoners feel in a language that resonated across the city. That’s what I believe he would do as Mayor - leading from the front and bringing people together instead of practicing the old-style, divisive politics that drives people apart.

Just as in the leadership contest, in London we need a fresh candidate who has broad appeal across the electorate. David is that candidate, and he’s building support across the party and across the city.

That’s why we’ve brought together a team of prominent figures and ordinary Londoners from across our city to advise David on his campaign. It includes leading figures in the London Labour Party like Catherine West, the former leader of Islington Council and now MP for Hornsey & Wood Green, and Stephen Timms, one of the biggest unifiers in the Labour Party, as Vice-Chairs. But this isn’t going to be a board full of political insiders. It’s going to be representative of the city David wants to lead – not just small segments of it. It also includes senior figures from the business world, cultural leaders and ordinary Londoners. It’s part of David’s determination not to appeal just to a narrow base but to reach across London as a whole. He is the only candidate who can do that to win us the mayoralty next year, and I’m delighted to be supporting him in delivering new leadership for a new London.