The first time I saw Ed Miliband live was at Latitude Festival, where he and 10:10 founder Franny Armstrong were doing a Q&A on the response to the threat of climate change. At that time, I had only been a member of the party for a few months, and I don’t think I really appreciated how well he did, assuming this sort of event to be more popular among politicians than it is in reality. The questions came from dedicated environmental activists, and got right to the heart of areas where government policy just hadn’t quite reached yet. “Would you support a ban on domestic flight?” “How do we stop state-owned banks investing into companies that are devastating the Canadian oil sands?” “Must we go nuclear?”

Franny naturally encouraged people to challenge him, but at the end of the session, she made a couple of important points. Firstly, she highlighted the Britain’s Low Carbon Transition Plan, which detailed exactly how Britain would meet its legislated commitments to reduce emissions by 34% by 2020, and by 80% by 2050. She said that the assembled crowd should not underestimate how much of a step the Department of Energy and Climate Change, with Ed at the helm, had taken with these moves. She then remarked that Labour were clearly going to lose the next election (prescient). But she also remarked that in the next few years, climate change and sustainable living were going to creep up the agenda, as it would become harder and harder to ignore the effects of unpredictable weather and dwindling resources.

Turning to look at Ed, she said “in five years time, those factors could be what make you the next Prime Minister.”

From this vantage point, a Labour Prime Minister, Ed or anyone else, feels a long way off. Labour is at an interesting point, where the party needs to find a balance between embracing and enhancing the positive changes made under the New Labour project – while also acknowledging its failures, and in so doing, re-entrenching the progressive values that we all care about into the heart of our vision for the UK. I don’t think any of us are naive enough to think that we have nothing left to do with regards to eradicating inequalities in health, wealth and social capital (far from it) – or that we haven’t done things which have alienated people who we used to count on to support us.

We need a leader who not only understands that, but who won’t be afraid to make that argument, to hold people to account, and to do it with fire and passion. We also need someone who will draw us all together on the progressive left – someone who understands that a healthy exchange of different views that spring from the same values is a good thing, and not something that should tear us apart. I’m not saying that the other candidates don’t have some of these qualities, and others besides – but Ed has them all in abundance.

In the months since that Latitude Q&A, we have all seen the qualities in Ed that will make him an inspiring, capable leader. He listened to eco activists who told him to consult with the wonderful Professor David Mackay (author of ‘Sustainable Energy Without the Hot Air’) on climate change policy, and ultimately hired him as an advisor. At Copenhagen, we saw him stay awake for days, and yet, he was sharp enough to act when he did to take control, halt proceedings, reassess the situation, and ultimately ensured that even though we didn’t get the deal we needed, we didn’t walk away with nothing, rather, we had something recognised and substantive to build on – plans for which were laid out in the ‘Beyond Copenhagen’ plan. When Gordon Brown was at his lowest ebb, Ed Miliband was among the first to leap to his defence, telling the circling sharks that people had underestimated Gordon his whole life, and that they shouldn’t make this mistake of doing it again.

And in the run-up to the election, the manifesto that he took a lead in authoring had real focus and ambition. This was notable in the area of welfare: “Are you for a residual welfare state that is just for the poor, which is the Tory position, or are you for a more inclusive welfare state? What the Tories are saying about child trust funds, child tax credits and Sure Start – they’re saying, ‘let’s residualise, let’s make the welfare state just for the poor’ but [this goes against] all the evidence in terms of maintaining public support [for the welfare state]. Why does Sure Start work as an institution? Because it brings people together.”

We have had some difficult weeks since we lost the election. But when Ed launched his leadership campaign, I was instantly assured of what I had known for some time – that Ed’s stall for Labour leader is already prepared: his brilliant track record – his willingness to listen, to evaluate and to act. And the early stages of his campaign – notably the launch of the Living Wage campaign – have assured me that he will practice what he preaches, and will take the entire movement with him.

I trust him absolutely with our future, and will support his campaign every step of the way.