In my interview  with him for the NS, Len McCluskey reserved some of his fiercest barbs for Peter Mandelson. With particular reference to the Labour peer, the Unite general secretary said of the Blairite grandees who have warned Ed Miliband not to "tack left":
It may be easy for these people, who are sitting with the huge sums of money that they’ve amassed now - they’ve done pretty well out of it, remember it was Mandelson who said he was comfortable about the filthy rich, presumably that’s because he wanted to be one of the filthy rich. But the fact is that under Labour the gap between rich and poor increased...that’s a stain on what Labour stands for.
Unsurprisingly, Mandelson felt the urge to respond. A Labour source informs me that the former Business Secretary declared at last night's Friends of Labour Students dinner that McCluskey was "the man who reminds us of where we came from and what we left behind".
But Mandelson's riposte is mild compared to that issued by Miliband, who accused  McCluskey of a "reprehensible" and "disloyal" attempt to divide the party.
McCluskey, whose union helped secure the Labour leadership for Miliband in 2010, told me that Miliband would be "defeated" and "cast into the dustbin of history" if he was "seduced" by "the Jim Murphys and the Douglas Alexanders". Of Liam Byrne, the shadow and work pensions secretary, he said: "Liam Byrne certainly doesn’t reflect the views of my members and of our union’s policy, I think some of the terminology that he uses is regrettable and I think it will damage Labour. Ed’s got to figure out what his team will be."
The irony of Miliband's denunciation  of McCluskey is that the Unite head has rarely been more well disposed to the Labour leader. McCluskey told me that he thought Miliband was doing "a very good job of holding the party together" and that while there were "disgreements" between the pair, he was happy with the course he had taken since 2010.
But it is precisely for this reason that Miliband felt it necessary to rebuke the Unite head so swiftly and explicitly. He couldn't allow the impression to form that he was willing to tolerate McCluskey's attack on the "Blairite" shadow cabinet ministers and the suggestion that they should either be ignored or sacked. As I noted in the piece, those associated with Blair are troubled by what they regard as Unite's excessive influence over European and parliamentary candidate selections. Rather than rejecting claims that the union had "stitched up" selections, McCluskey suggested to me that he was simply beating the Blairites at their own game.
The truth is that this is a process that was set up by Tony Blair, and the right-wing and organisations like Progress have had it their own way for years and years and have seen nothing wrong it.Because we're having some success, suddenly these people are crying foul. Well I’m delighted to read it. I’m delighted when Tony Blair and everyone else intervenes because it demonstrates that we are having an impact and an influence and we’ll continue to do so.