I think the fact that degree level education, still largely the province of the middle classes, is considered a pre-requisite for so many jobs these days, has meant that intelligent people from socially deprived backgrounds will never make it past a certain ceiling.
But isn't that the whole point of the increasing emphasis on getting the 'intelligent poor', as one Labour MP I heard describe them, is all about, Martin - along with the fact that increasingly the middle class is being made up of what would have been regarded as the 'working-class' in the past (ie, a plumber will often now be classed as 'middle-class' whereas 50 years ago, that would have been a working-class job). Rather than having a middle- and a working-class as in the past, we seem to have a middle- and an under-class now.