Why Theresa May will say we are leaving the single market and customs union

So you may read this morning's newspapers and think "oh my gawd, we're leaving the EU single market and its customs union" - because that is what most of them report the prime minister will announce in her important Brexit speech on Tuesday.

But you should not be shocked or surprised, because Theresa May has been signalling this unambiguously for months, even if she refused - some might say perversely - to say the actual words.

How so?

Well she has made crystal clear that her priorities for Brexit are that the UK regains control of immigration, that British law becomes independent of rulings by the European Court of Justice, and that we gain the ability to negotiate free trade deals with countries outside the EU.

Now all three of these priorities are in direct contravention of the rules of EU single market and the customs union.

So it was absolutely bleeding obvious that she would have to say at the start of formal negotiations to leave the EU, under Article 50 of the EU's treaties, that we are out of both.

May's Brexit plans may not align with the rules of EU single market and the customs union. Credit: PA

It is why global investors took the view months ago that, for a while at least, our trade prospects would suffer, and sterling collapsed.

But to be clear, in making the belated inescapable admission that we will not be formal members of either the single market or the customs union - such that we won't be a sort of non-voting EU member line Norway - that is where the interesting talks with the rest of the EU begin.

Because it is at that point that the rest of the EU has to decide whether it is in their interest to negotiate a different kind of free trade deal for their and our goods and services, whether to make these long and complicated talks rather than just replicating many of the existing arrangements under the single market and customs union, and whether to grant us a relatively pain free longish transition period where we continue to benefit from single-market and customs-union membership till the new deal is in place.

That is what I have been banging on about here since August.

Or to put it another way, Theresa May's big Brexit speech on Tuesday will tell us everything and nothing.