Earlier this week I explored the peculiar state of Labour’s latest stance on Brexit. Since then, as predicted, it’s continued to shift – Tom Watson is now flirting with the possibility of continued membership of the Single Market and the Customs Union after transition, a further departure after what was first a manifesto policy of leaving the Single Market when Brexit happens in 2019, then a policy of staying in after Brexit but only during transition. There’s no sign of them taking on a permanent or coherent form.

That lack of a clear alternative hasn’t stopped the Opposition laying into the Government’s red lines and approach to negotiations, of course. Yesterday, Sir Keir Starmer fumed:

“After three rounds of negotiations, real progress should have been made and in principle agreements reached on all phase one issues. Instead, the two sides appear to be getting further apart.

“The risk of not reaching the October deadline to move on to the main negotiations is now very real…

“Both sides need to redouble efforts and work together to reach a strong Article 50 deal and a close future partnership. If more negotiating sessions need to be added between now and the October deadline, they should be. Substantive progress and clear outcomes are urgently needed.”

As we know from his war on ambiguity, Starmer loves nothing more than clarity. So it’s a bit strange that, while demanding “real progress” and “in principle agreements”, with “substantive progress” and “clear outcomes” on the issues under discussion in this first phase, he and his colleagues have been largely silent on one of the central matters at hand: the Brexit bill. What amount would, in Labour’s view, constitute “real progress”, “a strong deal” and “clear outcomes”? Or, in other words, how much would Labour be willing to pay?

As ever, there have been several different lines in the past.

In April, Starmer told the press he would negotiate but “meet our international obligations” – signally refusing to rule out the figure which had been put to him, which was Jean-Claude Juncker’s estimate of £50 billion.

By May, Jeremy Corbyn was attacking the idea that the bill could only be negotiated after agreement on trade, setting out a position that would risk Britain deciding how much to cough up before knowing how high or low trade barriers would be with the EU.

Perhaps most troublingly, the Labour manifesto ruled out walking away at all, declaring “We will reject ‘no deal’ as a viable option”. In effect, that was a message to Brussels that a Labour government would take a deal at any price. If ‘no deal’ was off the table, Michel Barnier would be able to name his price and simply insist upon it.

Since then, while we’ve heard complaints about the Government’s proposals and the supposed lack of progress, Labour notably haven’t gone out of their way to discuss the Brexit bill at all. It’s not hard to see why – they know that the idea of paying very much at all is deeply unpopular, and if they went into it the question would inevitably come: well how much would you pay, then? Whether it’s the £50 billion that Starmer wouldn’t rule out in April, or the £100 billion that the EU is reported to be suggesting, or some larger figure, inflated by their deal-at-any-price manifesto commitment, the answer would not go down well with voters. Watson’s prospect of staying in the Single Market would mean payments continuing forever, rather than just paying a one-off bill at all.

One reason why there haven’t yet been the “agreements reached on all phase one issues” that Starmer demands is that the British negotiating team have rightly challenged the basis on which the EU is trying to calculate a vast bill. When the Opposition denounces the delay, they appear to be saying that this effort should not have been mounted. Would they simply have paid what was asked up-front, just to get on with it?