The consensus among the pundits seems to be that attacking the Tories for being posh - or "toffs" - is a legitimate tactic for Labour but has been ineptly done in the Crewe and Nantwich by-election.
Steve Richards says as much in the Independent today while in yesterday's Guardian Jonathan Freedland says that it would be ok if only Labour were truly meritocratic.
What always gets me is that people who defend public school privilege accuse their opponents of being anti-aspirational. Buying advantages is not about aspiration, it's about the keeping the already advantaged ahead of the aspiring. It is the opposite of meritocratic.
p.s. I've just come across a blog called class warfare which declares that it adheres to the Orwellian maxim: "During times of universal deceit, telling the truth becomes a revolutionary act."