So the Belgian government, not normally seen as a friend of the UK, seems to be doing David Cameron a big favour.

Presumably because it is exasperated with the UK's supposedly constant demands to be treated differently from other EU members, the Belgians, backed by the French and others, want the EU council conclusions to say that the new settlement for Britain is the final, immutable deal.

So if British people reject it in the referendum, there would be no coming back to Brussels to sort us out a better deal, prior to a second referendum.

Sources say David Cameron will not object to this "deal is the deal" statement in the summit text.

Ha!

Cameron's acquiescence is based on powerful self-interest.

Because some British critics of the EU have mooted that the way to get a better EU deal is for British people to vote down the one on the table in the referendum.

It makes voting to leave a cheaper, less scary option - because the leave vote would just be a bridge to yet more EU talks, rather than the definitive goodbye.

Boris Johnson leaving number 10 on Wednesday Credit: ITV News

As it happens, Boris Johnson - who I reported last night is on the verge of declaring for EU exit - is one of those who has suggested that a vote for leaving might not actually force us through the exit.

It is in the prime minister's interest, of course, for the referendum stakes to be - if not life or death - well unambiguously about whether we stay or go.

His best chance of winning the vote is to persuade us that it really, really will decide whether we stay or remain.

So he may be thinking of sending a thank you to Belgium's premier.

Except that Cameron may conclude that would be a mistake, because he would fear that the Belgians actually want us out of the EU - and they would hate the idea that insisting there can be no more special deals for Britain would actually bind us in.