There's an excellent article by Ed Balls in yesterday's Guardian which clearly states the Keynesian position. If you're not yet convinced it is well worth a read. Just a pity that Balls wasn't quite so openly enthusiastic about it when he was an influential part of the government.
Saying one thing in government, than another in opposition (or vice versa in the case of the Liberal Democrats) does little to enhance the reputation of politicians or increase respect for the democratic process. It is now nearly three months since the election, but there is as yet little sign of the promised "new politics" - alas, just the mixture as before.