As Ben Brogan has pointed out, if the GH/PH plot was not conceived with the say-so of Peter Mandelson (or at least the nod) then it won't be going anywhere.
At the same time, if Mandy tells Gordon that he must agree to the secret ballot then he will find ot very difficult to resist.
But this really is the crunch time for the Labour Party. If it wants to avoid a decade of wilderness it needs to nail this issue once and for all.
The point is that David Cameron knows that the Prime Minister is his greatest electoral asset and without him all bets are off.
It has become the lazy orthodoxy that Brown is the problem - lazy because it allows backbench MPs to avoid taking repsonsibility for the future of their party.
This is one of those once in a generation moments (like the Granita dinner), when the whole history of the country could shift - and again Peter Mandelson is the key broker.