Here’s my take on why Blair has decided to go for a referendum (and none of this is with hindsight – I’ve spent the past fortnight trying to interest papers in a column saying that he’d go for one; no one, of course, was interested!).

Given his difficulties over Iraq, people seem to have forgotten just what a political genius Blair is; what a master tactician; and just how much and how often he is prepared to gamble when the stakes he has been dealt look awful. He is far more capable than any previous PM of turning a non-existent hand to his total advantage. Look, for example, at how in opposition he made Labour – Labour! – the most trusted party on crime and the economy.

As for gambling, there’s the example of Iraq itself. And remember his first act as leader? Announcing at the 1994 Labour conference the abolition of Clause IV, which went to a vote which for most of the preceding months the commentariat were assuring us he would lose (I remember in particular a Guardian analysis of the likely voting which showed how he couldn’t possibly win the vote).

His reputation is now severely damaged as a result of Iraq and the failure of any significant public service reforms. So he has two options for the constitution: try to force it through (which he may not even be able to manage in the Commons, let alone the Lords) and then leave office despised on the three fronts which matter to him (EU, reform, and Iraq); or adopt the ‘with one bound, he was free’ tactic, and allow a referendum.

(Don’t forget that there are likely to be more Tories and fewer Labour MPs after the next election. Add to that the fact that the safest seats are in the hands of Old Labour types who are more likely to rebel than the careerist Blairites, and there is no guarantee that he could win a vote in the Commons. A referendum will thus, paradoxically, make ratification more likely, since a ‘yes’ vote would not be overturned in the Commons.)

The downside for him – of course - is that he might lose a referendum; but then he might lose without one, too.

The upside is that the moment he announces it, he gets 10/10 from the media and the chattering classes for doing the right thing; he opens up the possibility of regaining trust and goodwill from ‘the people’; and – crucially for him, given his Europhilia – he makes possible the final settlement of the European question for this generation. And he does it by a mechanism in which the odds are stacked in his favour.

There's a further factor: the chances are that this is all academic. First, there's no guarantee of a deal at Brussels. But even if there is such a deal and the constitution is agreed, there's every possibility that one of the other countries which is having a vote will throw the whole thing up in the air by voting 'no', which would mean Blair gets all the credit for offering a referendum and 'listening' - I guarantee that we'll here that No10 buzzword in the statement announcing a referendum - without having to have the actual thing.

All of the above notwithstanding, I still think – and hope, if the constitution is much like the existing document – that there’d be a ‘no’ vote here. Just because the poltics make sense doesn't mean he'll get the result he wants.