Earlier quoted context omitted.
Except many exist today, and there mostly populated by the middle class with ridiculously low levels of poor people. Like 1% on free school meals and majority were tutored for the entry test? Most poor people can't afford tutors. With stats like that, they REINFORCE class structure, not break it. And do poor people want to pay for the education of the elites? Which is what current grammars effectivly do.
That is only because there are so few grammar schools left. When they were all over the country, anyone who passed the 11-plus, regardless of their family's wealth, could go. These days they are intended to reinforce class structure. You don't need a left-wing, if you don't have a poor working class...
The only reason for populist support for them at the moment(Daily Mail, Telegraph, UKIP, BNP and other populist parties all support them), is most people THINK their kids will get in although most won't(By definition). When they come realise that, populist support will disappear again, and they will go out favour once again.