Ahead of tonight's Newsnight special on the coalition (at 2230 on BBC Two) it is worth asking a big question:
Were Conservative MPs railroaded into accepting the coalition on the basis of a lie, or at best an unfortunate misunderstanding?
That's the allegation which has been swirling round among Tories at Westminster for several weeks now.
One Conservative MP - far from a right-winger - reckons David Cameron lied to the shadow Cabinet and his backbench MPs at least four times in the hours leading up to the coalition agreement with the Lib Dems on 11 May.
The big issue is whether the Conservatives needed to offer Nick Clegg a referendum on the AV voting system.
Mystery especially surrounds what happened on the afternoon of Monday 10 May.
I recall William Hague emerging from St. Stephen's entrance of the Commons with the surprising news that the Tories would now offer the Lib Dems a referendum on AV.
I suggested to Hague that the Conservatives were now merely matching Labour, who had been promising a referendum on AV since Gordon Brown's speech at the 2009 Labour conference, and included it in their 2010 manifesto.
Oh no, Hague told me, he understood that Labour was now offering the Lib Dems AV WITHOUT a referendum.
I must admit Hague's comment disconcerted me. I failed to follow it up, simply because I feared I was uninformed and that Labour had made this promise during the course of the day and I hadn't noticed.
And it's now clear from several government Tory sources that David Cameron told both his Shadow Cabinet that afternoon, and the meeting of all Conservative MPs that evening, the same thing. His argument was that they had to do something to catch up with Labour's offer to the Lib Dems of AV without a referendum.
But it wasn't true. There's no evidence that Labour ever offered the Lib Dems AV without a referendum. Indeed it's hard to see how the Labour leadership ever could have got Labour MPs to go along with such an idea.
Among those Conservative MPs who recall being told by the party leadership that Labour was offering AV without a referendum was Julian Lewis.
And during the Commons debate on the Queen's Speech, on 7 June, he raised the matter with the Shadow Justice Secretary Jack Straw:
Dr Julian Lewis: Will the right hon. Gentleman [Jack Straw] confirm that in the course of the competitive negotiations with the Liberal Democrats as to which side was going to form a Government, his party offered the Liberal Democrats a deal whereby AV would be rammed through this House without a referendum?
Mr Jack Straw: The answer is no. I would also say to the hon. Gentleman that a very significant proportion of Labour Members, including myself, would never have accepted such a proposition had it been put forward - let us be absolutely clear about that.
(Hansard 7 June 2010, cols 29-30)
Astonished to get that response, Julian Lewis then pursued the issue with Nick Clegg later in the same debate:
Dr Lewis: ..... He will have heard the answer that the right hon. Member for Blackburn (Mr Straw) gave when I asked him whether it had been the case that the outgoing Labour Prime Minister had offered, during the coalition negotiations, to ram through the alternative vote without a referendum. I am not giving away any trade secrets when I say that Conservative MPs were told that that was the case. The Deputy Prime Minister is in a position to know. Were the Liberal Democrats offered by the Labour Party the alternative vote without a referendum? Can he set the matter to rest?
The Deputy Prime Minister: The answer is no. The right hon. Member for Blackburn (Mr Straw) was right. That was not offered by the Labour Party in
those discussions. The hon. Member for New Forest East (Dr Lewis) is right - I should know whether it was offered or not.
(Hansard 7 June 2010, col 44)
So where did the story about Labour offering the Lib Dems AV without a referendum come from?
There are several possibilities.
In their talks with the Tories did the Lib Dems over-egg, exaggerate, or even lie about what Labour had offered them?
That's certainly the view of at least one Conservative minister who is very hostile to the referendum.
Or did the Conservatives simply misunderstand what the Lib Dems said they were being offered by Labour?
Alternatively, did David Cameron and his senior colleagues simply invent Labour's offer in order to cajole Tory backbenchers into accepting they should offer Lib Dems the AV referendum?
There's one other intriguing possibility - which some Labour people suspect may have happened - that in a desperate moment Gordon Brown privately offered Lib Dems AV without an referendum, but failed to tell Jack Straw or any of his other colleagues or the Labour negotiators about his offer. In any case, Nick Clegg denied that in the Commons.
Meanwhile another of David Cameron's claims also aggrieves many Conservative MPs as they become increasingly concerned about the coalition.
In his meeting with Tory MPs on the Monday evening, David Cameron said the party had no option but to go into coalition with the Lib Dems, and that a minority government wouldn't be viable.
And yet only two days later, in the famous press conference in Downing Street garden (misnamed the Rose Garden press conference), Cameron claimed he could indeed have gone it alone, but much preferred a firm coalition with the Lib Dems.
"We could have had a minority government backed by a Confidence and Supply arrangement but thought this is so uninspiring, it might last for a month, six months or a year but it won't do what we want to achieve..."
As the arguments about AV and the coalition get increasingly heated over coming months, the mysteries of who said what during those few fascinating days may be worth a lot more examination.
Watch a special edition of Newsnight about the coalition government on Monday 26 July 2010 at 10.30pm on BBC Two.