Labour have unveiled a new approach to Brexit – or, at least, a newish approach. The Opposition wants a four-year transition arrangement, during which Britain would remain a full member of the customs union and the single market.

The announcement isn’t that drastic of a shift from Labour. What really divides the party is on the shape of the deal after Britain’s exit from the European Union is over, where there is agreement over what words to say, but disagreement over what those words mean.

What Keir Starmer has done is more of a clarification – we knew that Labour supported a transition, we didn’t know what that transition would look like or how long it would be – than a change of policy. Thanks to the loss of the Conservative majority, Labour can, in concert with the other opposition parties, enforce its will on the shape of negotiations provided some Remainer Tories are willing to vote against the government.

As it stands, both the major parties support a fairly drastic exit from the European Union, but the Conservative position is several degrees of magnitude harder than Labour’s, as it would involve shucking off the judgement of the European Court and leaving bodies such as Euratom and the customs union.

So why does the new policy matter? It’s true to say that the Conservative policy of a two-year transition is basically “take a breath and then have a hard Brexit”, while Labour’s policy is basically “take a deep breath and then have a hard Brexit”, but the reason why Brexiteers are nervous about the change – Brendan Chilton, the head of Labour Leave, took to Twitter to vow to fight to prevent the party softening its position – is that a lot can happen during a deep breath.

For one thing, every year that Britain’s transition agreement lasts is a year that, demographically speaking, the country becomes more pro-Remain. The electoral incentives start to tilt in favour of a government adopting the Liberal Democrat position of a vote on the final deal or a return to Britain’s full membership of the EU. There are a number of obstacles to that, not least the question of whether the 27 member states of the EU would all agree to allow the United Kingdom back into the fold. But it is plausible enough that you can see why it occupies a place in Brexiteer demonology and why many Remainers are putting their hopes in it.

(There’s the added factor, too, that the economic indicators all make it more likely than not that the next election will produce a Labour government, which will either be dependent on its own Europhile wing or the Liberal Democrats and its own Europhile wing. A transition deal that stretches past the next election on 5 May 2022 is significantly more likely to become forever or be the scene for a U-Turn into full EU membership.)

So while Labour’s position is, in of itself, some way away from a soft Brexit or no Brexit at all, it makes the possibility of a soft Brexit or a return to the EU more likely.