I have been speaking to Quentin Davies (watch the interview here) and what I've been told is that he and Gordon Brown have been talking frequently over a period of months. Remember that Mr Davies has long been at odds with the Tory leadership over Europe, and he was highly critical of David Cameron's decision to break with the EPP (the alliance of conservative parties in Europe), and he'd started to become more and more outspoken on that issue.
He knows Mr Brown because he has served on the Treasury Select Committee, so the two men already had some sort of relationship, and I'm told they bumped into each other a few months ago, got chatting, and that Mr Davies talked about how he admired one of Mr Brown's speeches... and Gordon Brown, ever with his eye on the political opportunity, invited Mr Davies in for a longer chat.
In recent weeks more of those chats have taken place, and finally, yesterday, Mr Davies decided to defect, and to write a to Mr Cameron - which reads, frankly, like it was written by Labour Party HQ, though we're assured it was written in its entirety by Mr Davies himself.
This is bad for David Cameron - not because Quentin is a household name (he's not) - but because it gives people the opportunity to hear from a Conservative (or at least, a former one) a list of all the reasons Mr Cameron isn't fit for office. It puts him, frankly, on the back foot.
But will the Conservatives miss Mr Davies as an individual MP? Probably not.
I'm racing to Gordon Brown's House of Commons office. Cameras have been summoned there to record interviews in relation to a mystery, but major, political annoucement expected any minute.
I wonder if it's a defection? Certainly Brownites are saying they intend to make the political weather from now on...
More later...
UPDATE 1448: It is a defection. But not one of the biggest. It's Quentin Davies - pro-European Tory MP. He's repeatedly with David Cameron about plans to leave the .
The place maketh the man. To understand Gordon Brown you just need to go to Kirkcaldy - the town which he represents in Parliament and in which he was brought up as the "son of the manse".
I recently spent a couple of days there with Mr Brown talking to him about his upbringing, his home, his schooling and the the rugby accident which cost him the sight in one eye. (You can watch the film I made about this by clicking here).
As we moved from place to place in the town he was stopped by people who'd been to school with him or played rugby with him or who had known him since he sat in the pews listening to his father's sermons. What it made me realise is that whilst on the national political stage he's been a private man, sometimes awkwardly so, he has always been on public display in Kirkcaldy.
The son of the minister, the boy so bright that he went to secondary school at 10 and University at 16, the sportsman who lost the sight in one eye and has feared blindness ever since has always felt watched and assessed as to whether he lives up to his father's values.
Brown is nervous of this story merely confirming suggestions that he is dour, thrawn (watch the film for an explanation), over academic and religious. So much so that again and again when I asked him to tell stories he would insert a reminder that he'd played tennis, football and rugby before his accident.
There were moments though when he could not control and calculate his answers. At one point - not as it happens in the edited film - I asked him whether he would finally feel he'd lived up to what his father expected of him. I couldn't help noticing that his eyes visibly moistened. Tomorrow Gordon Brown will care what the voters, his fellow politicians and what the media think of his arrival at Number ten. I suspect though that he will also be pondering whether the Rev Dr John Brown would approve of what he was saying and planning to do.
