What, other than the fact they are both trade unions, connects the National Farmers’ Union and Unite? The answer is that both represent workers who are on course to lose out from Brexit and that neither feel able to explicitly call for the result to be overturned.

That essential truth is a vital part of understanding the politics behind Unite president Len McCluskey’s intervention for the New Statesman, in which he said publicly what he has been telling Labour MPs privately: that another referendum risks blowing the next election for Labour.

He has left himself plenty of wriggle room to support a Remain vote should that contest happen – remember that Unite’s position in that referendum is not in McCluskey’s gift but of Unite’s executive committee – but made it clear that as far as he is concerned, another vote is a big risk for Labour and a potential disaster for the country.

One of the reasons why the referendum went the way it did is that people working in farming and manufacturing voted in a way that it is not immediately clear aligns with their economic interests. Both the carmakers represented by McCluskey and the farmers represented by NFU president Minette Batters have much to lose by leaving the single market and the customs union. Yet the NFU had to restrict itself to a pre-referendum statement to members stating that although it thought that continuing membership of the European Union was best for British farmers, it would not actually campaign for it.

Most British trades unions backed a Remain vote, but with a handful of exceptions they found a hostile response on their shop floors, and none report any real shift in priorities among their members. (Which is what we’d expect from the polls, where the shift to Remain is based on fading enthusiasm among Brexit voters and the entry of new Remain voters into the electorate thanks to demographic change.)

Anyone who thinks that McCluskey’s intervention is because of some deference on his part to Jeremy Corbyn needs to find a way to reconcile that analysis with the Labour Party’s row over Heathrow, which Corbyn thinks is an environmental calamity and John McDonnell has made it his personal mission to oppose airport expansion as one of the MPs whose constituency is directly under the flightpath. Unite has shown remarkably little compunction in voting to undercut the leader’s office when their interests conflict. The difficult truth for anyone who would prefer to see Brexit overturned is that McCluskey’s balancing act on Brexit has as much to do with his day job as head of a trades union as it does with the game of Labour power politics.

It further underlines the fraught parliamentary path to a second referendum as well as the difficulties of winning the rematch. We know that Nicky Morgan, Nick Boles and Jonathan Djanogly won’t vote for it. We know that a sizable number of Labour MPs – it’s worth noting that Gloria De Piero, no one’s idea of a Bennite or a Brexiteer for that matter, approvingly shared the piece on Twitter – won’t vote for it.

So why do supporters of a second referendum think they have a shot? They take comfort from the fact that Amber Rudd has become the first cabinet minister to basically echo what McCluskey is saying – telling Robert Peston that while another referendum isn’t her preferred route, she might reluctantly back one if needed, but that MPs ought to find a way forward to negotiate a Brexit deal – and think that, when push comes to shove, Labour opponents of another referendum will choose it over no deal.

But will they? It feels equally likely, given that we know that Corbyn is not going to expend a single penny of political capital arguing for another referendum, that Labour MPs who fear no deal but don’t want to risk another referendum will use his remarks as cloud cover to explain why they are, reluctantly, voting for the withdrawal agreement the second time around. (Assuming that is, that the Labour leadership decides that it is better off casting itself as the victim of Labour MPs voting for the agreement rather than the agent of a compromise in the national interest. Both schools of thought are represented in the inner circles of Labour power.)

Add that to the growing number of pro-Brexit Conservatives who are realising that the chances are that rejecting the withdrawal agreement only ends with a softer Brexit, and you begin to understand why Tory supporters of May’s accord are starting to perk up a bit as parliament shuts up and heads off for the Christmas holidays.