Departing from script in his speech to Labour conference this morning, Keir Starmer won a standing ovation when he said the party was not “ruling out Remain as an option” in a hypothetical second referendum.

In doing so he has picked a fight with a powerful adversary: Unite. In the hours after the shadow Brexit secretary spoke, both Len McCluskey, the general secretary of Labour’s biggest union backer, and Steve Turner, his assistant, said any referendum would be on the terms of the deal and that Remain would not be on the ballot.

McCluskey has made that point repeatedly in recent days. Those involved in drawing up the conference motion – a process that saw Starmer, local party delegates, and the unions hammer out a compromise motion – dispute his line of argument. A line stipulating that any public vote would be on the terms of Brexit, rather than Brexit itself, was removed during Sunday night’s compositing meeting.

Unite’s aversion to a second EU referendum that explicitly includes the option of reversing the result of the first highlights the defining anxiety of Labour’s Brexit debate. McCluskey has said that Labour’s path to a majority runs through working class communities in the North and Midlands that, by and large, voted Leave. In July he urged Corbyn to “test every policy against how it is going to play in Walsall and Wakefield, Mansfield and Middlesbrough, Glasgow and Gateshead” and not rely on gains in London to deliver a majority.

Accordingly, the leader’s office is focusing its campaigning efforts on towns in England, both in its former industrial centres and on its coasts, as well as in Scotland. It is also defending slender majorities in Leave-majority seats like Dudley North, Newcastle-under-Lyme, and Ashfield in Nottinghamshire. It’s not the economy, stupid, but the towns. Sources close to Corbyn say this year's conference is "its most direct pitch yet to people in post-industrial towns and communities" and “the millions of people who have been most directly affected by deindustrialisation and austerity”.

This is the context within which McCluskey’s aversion to including Remain on the second referendum’s ballot paper should be understood. The (justified) fear is that it would prevent Labour gains and hasten losses in places it needs to win at the next election. Instead, McCluskey told a fringe event on Sunday, the party should look to unite Leavers and Remainers after a general election rather than divide them again with another in-out referendum. It remains to be seen whether Labour will be given a choice.