How about this as a scenario? Alistair Campbell arranges for the McBride/Draper emails to be leaked to Guido, in order not only to mortally wound both M & D (and neutralise Charlie Whelan for some time to come), but mainly to destabilise Gordon Brown ("how could he not know", "it came from Number 10's system", etc) so that a fresh leader can be installed in preparation for the 2010 General Election. "A cleansing of the Augean stables - New Labour has put its house in order - renewed commitment to our core programs - it was always about policies, not personalities - our narrative was temporarily hijacked by psychologically flawed mavericks" and so on.
Has Guido been used?