Later this week, Theresa May will say she wants a "customs arrangement" - or what today’s FT brands, unfelicitously, "a European traded goods area" - with the EU, in apparent distinction to Labour's "new customs union".
How real and significant is the difference? And would either proposal find favour with the rest of the EU?
Both ideas are designed to obviate burdensome border checks on imports and exports - and are intended to prevent a peace-undermining re-establishment of a hard border between Northern Ireland and the Republic, to reassure manufacturers that they will still be able to ship parts cheaply and easily to and from the rest of the EU, and to prevent huge traffic queues of lorries building up at Dover and other ports.
But the EU is likely to look askance at both what the Tories and Labour want.
In the case of the Tories, the EU would want to retain the right to do third party trade deals.
And in the case of Labour, they would want both to influence the EU’s own third party trade deals and then opt out of any they don’t like (like TTIP with the US).
The problem for Theresa May is that her plan is the only one the EU actually has to take seriously - and in the meantime Labour can have its gateau and eat it by claiming to offer something more pro-Europeanly plausible and realistic (even if that is disingenuous).
For what it’s worth, my Brussels sources don’t see Mrs May's European Traded Goods Area, and her hope of a "mutual recognition" deal for City firms, as a remotely plausible basis for trade negotiations.
So given where the weight of opinion is in parliament, at some point a British prime minister (NB I am not saying who that would be!) will probably have to start taking seriously the idea of the UK applying to stay in "the" not "a" customs union - with all the alleged affronts to our independence and sovereignty that would entail.