There's a complete transcript of Blair's interview last week on European Voice.
Blair argues that the decision to promise a referendum last time was based on what the public "believed" (wrongly) and the fact that "there wasn’t really an alternative". It also seems to have hinged on the use of the word "Constitution." So much for high principle.
…where is the difference between the constitutional treaty and an amending treaty?
I think once you decide that you are going to as it were have one consolidating treaty and then a whole series of things, albeit things that in some ways you can say have their traditions in existing European treaty or in European traditions of one sort or another, I think you are into a different, you know you are arguing about something different for people. I mean I made exactly these arguments myself two or three years ago, but in the end I am afraid you have got to accept people believed that what they were getting was something fundamentally different from a normal conventional treaty, and you know one of the things in politics is you have got to listen to public opinion and I think here, but also elsewhere in Europe, people said well if it is something that you are describing as a constitution for Europe in that sense for the first time, in that way, that is something significantly different for us.
You didn’t have to call a referendum, you did it and that put other leaders under pressure to organise a referenda with the results that we know. Do you regret that?
No, because there wasn’t really an alternative. Because you have to deal in politics with what people perceive and if you say we are getting rid of all the previous treaties, we are now having a treaty that is a constitution, people will look at it differently, and they did.
It also sounds like the UK has been leading on the Poles to kick off about the institutional deal (which basically makes it easier to pass more regulations). But it doesn't sound like Blair is exactly going to support the Poles to the hilt:
Your Polish colleague has suggested that he would count on support from your side for a change in the voting system and for the reduction in the field of qualified majority voting. Would Great Britain support Poland to change the voting system?
Well look all of these issues we have to discuss, although we went through a very complicated process to get to the voting system. That is different from the QMV issue. But rather than as I say negotiate in public, I think the basic principle for me is we have got to accept you won’t get agreement, I don’t think, to a new constitutional treaty, what you can do is get agreement to a conventional amending treaty, a simplified treaty, that gives you the rules that make Europe more effective. Now exactly how that leaves you on voting and all the rest of it, that is a matter to discuss.
There is a nice look at some of the logical contortions in the interview on the Economist's "Certain ideas of Europe" blog.
In summary, if I have this right, the constitution was good enough that Mr Blair would have been happy with it, but not good enough that anyone was going to vote Yes on it in any future referendum, which is why it was important that no-one else should be allowed to vote on it, or any mini-version of it, and especially important to make that clear before the French people had a chance to vote and elect a president who might be minded to give them a vote on any version of it. And Mr Blair knew he had to do all this, because that is what he heard the people telling him. Oh, to have the hearing of a prime minister.