The draft document now in the public domain had a very limited circulation. Members of Labour's National Executive that I have spoken to hadn't seen it.
Most - though not all - shadow cabinet members were shown only the sections which related to their policy areas - to prevent leaks.
And certainly the leak of a complete version of a draft manifesto before it has been formally discussed is unprecedented.
Sources close to Jeremy Corbyn say "100%" they did not leak it and were shocked around 20:00 BST on Wednesday to find out it had leaked.
And sources close to both the party leader and the Unite leader Len McCluskey are trying to point the finger at the party's deputy leader, Tom Watson.
They say this is all about 9 June. If an impression of chaos around Mr Corbyn is created now, and Labour fails to get 30% of the vote on polling day, it will give his deputy a reason, or excuse, to call for the leader's resignation.
But Mr Watson has categorically denied leaking the manifesto - and his allies say it would have been mad to do so. They see this as an attempt to damage his reputation as he wouldn't want Labour to perform badly at the forthcoming election.
And they say the Labour leader's office had accepted that they hadn't leaked, because the version of the manifesto that Tom Watson had in his possession wasn't the version that made its way to the papers. And sources at the Daily Mirror have made it clear to the BBC that Mr Watson was not the source of the leak.
Other Labour sources are pointing out that union officials saw a draft on Wednesday but Labour now hopes that the debate will move on to substance rather than the internal soap opera.
It's not just Labour's policies that have been exposed by the leaks of the manifesto - it's the level of distrust at the very top of the Labour Party.