Nick Clegg’s devastating attack on Gordon Brown today signals the next stage in the informal agreement between a coterie of LibDem and Labour senior boys: that if the Cleggies drop their commitment to STV PR, the ‘Mandybands’ will dump Gordon.

At first sight, it looks as if Nick isn’t really using his political noddle overmuch on this deal – it having been struck prior to his surge. Practically all the big Labour beasts want shut of Gordon: it’s just that none of them had the spine to do it before the election. As the deal stands now, the Party with under a quarter of all voting intentions is going to stay in power and get rid of the main piece of electoral anti-matter they’re carrying. So what is Clegg getting out of this?

I don’t know the answer for certain, because formerly talkative LibDems are suffering a severe case of lockjaw at the minute. But educated speculation is just as much fun – and would reflect what one Whitehall and two Westminster contacts have put to The Slog in the last 24 hours: Nick Clegg thinks that what’s in it for him is the key to Number Ten Downing Street.

A week ago that would’ve sounded far-fetched – but not now. This is a dream ticket for both sides: Clegg becomes PM and his mate gets the Chancellorship; Mandelson stays at the centre of power as Lord of everything and nothing…. and shafts arch-enemy Ed Balls. (Andrew Neill is, as I write, making this exact point on The Daily Politics.)

What could go wrong? And the answer, of course, is everything – Cameron making Clegg look like the lightweight he is in the forthcoming debates, for example. The Labour vote collapsing entirely – which it shows signs of doing. Other as yet unforeseen events. And most pointedly, Miliband asking “What about me?” (He should also be asking “What about my mate Darling?” but that’s not the way Miliband works.) The most likely outcome is that David Miliband will be suitably stroked and left at the Foreign Office.

Stay tuned for what the Tories must now obviously do – apart from turn the heat on Clegg’s policies. Meanwhile, over at the BBCNews site, the other Nick (Robinson) is still asking whether Gordon is ‘a barrier’ to the LabLib deal. This must be frustrating for Nick, who is far too well-informed and intelligent to be this far behind the music. Sadly, he has the arm-biting BBC Chief Mark Thompson on his back.