Labour conference has finally reached a conclusion on the Green New Deal, the radical climate policy that's been subject to as much internal wrangling as Brexit over the past few days here in Brighton. In a floor vote early this afternoon, delegates overwhelmingly voted for a version of the plan that would see a Labour government commit to achieving net zero carbon emissions by 2030.

What does that tell us? In some respects, nothing much: we already knew that the Green New Deal would be the hottest conference topic as far as constituency party delegates were concerned. The number of motions calling for Labour to adopt a version of the policy far exceeded any other submitted by CLPs – even on Brexit. That it ended up passing overwhelmingly is unsurprising.

But what is interesting is the form the policy ended up passing in. Over the weekend, two lengthy compositing meetings – the process by which the trade unions, party leadership and conference delegates thrash out an agreed compromise wording – broke up without consensus.

The long and short of the failure to reach agreement was the big unions, specifically the GMB, thought the wording favoured by activists – which originally included a demand for zero, rather than net zero, emissions by 2030 – called for too much too fast. There were also serious anxieties about its demands for an end to fracking and airport expansion.

In return, the GMB proposed a notional compromise that lacked a date for achieving zero emissions, or, indeed, any binding commitments at all – instead, its language was largely aspirational. That was never going to be enough for most grassroots delegates. But nor was their ambitious first preference ever likely to fly: a 2030 zero emissions target isn’t even a demand of the US left activists from whom the Labour Campaign for a New Deal took their inspiration.

Instead, they moved to the less ambitious – but, by the standards of UK climate policy, still radical – target of net zero emissions by 2030, the preferred position of the Fire Brigades Union, which sponsored the eventually successful motion. The FBU has long had a radical agenda on climate change and at its last conference adopted a policy more or less identical to the motion passed by Labour delegates today.

What does the outcome of the horse-trading tell us? As well as illuminating the divergent interests of the big unions and the grassroots, it also shows the limits of their ability to dilute policy propositions they don’t agree with. And the FBU’s central role in getting a stronger iteration of the policy than might have been expected over the line is testament to the influence that the smaller, Corbynite unions can wield in these debates too.