In reply to dissonance:
Ok i'll work backwards on this one: what I think is wrong with what you might call "career politicians" is that they are indoctrinated with a philosophy at an early age Ed and Dave Milliband appear to be prime examples. They then chart out for themselves a career path leading to a role in politics, which includes a politics related degree (therefore they decided to enter politics with their embryonic political philosophy before even leaving school), and several years working as a gofer with the party of their choice, before eventually making it onto the public payroll either as an MP, advisor, quagocrat, etc. My problem is that they are driven to become an MP most likely only associate with like minded people at uni and in the political bubble. This is in no way a rounded development.
Someone entering politics later has had a little more time in the, hate this term, real world, encountering people of different backgrounds and views, having their political convictions challenged not reinforced by their peers so when they do go into parliament they are going with their own set of convictions (rather than daddy's) and less likely to be a party drone. Also more likely to have entered parliament as a duty rather than as a career path.
I am not arguing that politicians should be technocrats though, when I say experience I don't think business owners for example are any better suited than metallurgists. The most desirable attributes fr me are integrity and a political philosophy developed over a lifetime of experience