A Tweet from Kevin Magure, a Brown supporter, says it all:
Long time since I've seen a political gift as good as Darling's "Forces of Hell" to Cameron who'll open it at PMQs
How Cameron plays this at PMQs is fundamental, especially after his tactical mistake of earlier this week. He must make no attempt to link Darling’s outburst with the bullying allegations.
Cameron would do well to recall the budget that Roy Jenkins produced just before the 1970 election:
It is though, generally assumed that Labour's defeat in the 1970 general election was partly the consequence of one month's bad trade figures announced a few days before the election and his delivery of a fiscally neutral Budget shortly before the election.
In other words, Jenkins produced a fiscally responsible budget rather than a political one. As an aside, it is one of reasons why he never became leader of the party.
The debate that is happening at present, similar to the one that happened in 1970 between Downing Street and the Treasury, may well have sparked off Darling's comments last night.
It is that divide that Cameron must concentrate on at PMQs.