For the second year running, the big story of Labour conference – as far as the visiting media is concerned – is the party’s intractable internal debate over Brexit. But grassroots activists are just as het up about another issue: the so-called Green New Deal.

Motions calling for the party to adopt the policy – the central planks of which are a massive programme of green energy investment, an end to airport expansion and fracking, and a commitment to achieving net zero carbon emissions by 2030 – were by far the most popular submission from constituency parties ahead of conference, even ahead of Brexit.

So on paper, a Green New Deal looks to be the sort of policy that could generate a broad consensus across the labour movement: on top of its healthy support among activists, it is backed by several shadow cabinet ministers, and is in essence a more ambitious – and, given its US-inspired moniker, trendier – iteration of the green jobs investment programme Jeremy Corbyn announced in his conference speech last year.

Yet agreement on just what sort of Green New Deal motion should be voted on by conference delegates has not been forthcoming. Last night's compositing meeting – the process by which representatives of the party leadership, trade unions and activists sift through every motion and come to an agreed compromise wording – broke up in the early hours of this morning without having reached a consensus.

Why? Because the unions, and in particular the GMB, believe the grassroots motions go too far. They think sweeping action against fracking and the aviation industry and the ambitious 2030 target, which is sooner than even high-profile proponents of the plan in the US such as Alexandra Ocasio-Cortez have called for, will harm the interests of their members. Instead, they are pushing for wording that – in line with the TUC’s climate policy – does not include a date at all.

Though the meeting will reconvene this evening, it is far from clear whether a form of words that satisfies both the grassroots and the unions will – or, indeed, can – be settled upon. Divisions and uneasy compromises between the leadership, membership and trade unions on environmental issues are far from new. Remember the decision to give Labour MPs a free vote on Heathrow expansion last year – a sop to Unite when the letter of party policy dictated they really should have whipped against.

But the torturous debate over a Green New Deal this weekend exposes just how divergent those interests are. More worryingly, it underlines that the path to an agreed policy on climate ahead of the next election – where most MPs agree it will be a vote-moving issue, especially among already disenchanted Remainers – will be far from straightforward.