I don't know how Peter Hitchens could keep a straight face on Question Time when he stated that what concerned him most about the current state of education is how dire it is for the poorest, and then in the next breath claimed that what would help is the reintroduction of academic selection. What he really means is that it would help a very modest minority of the poorest. The sole conclusion it's possible to draw is that Hitchens only places any value on the poor if they happen to be fairly bright - the others don't seem to even have an existence in his mind. Now, academic selection would of course also be massively advantageous for the majority of more affluent children, but I'm sure that's nothing more than a extraneous detail in his thinking. We know it's those poverty-stricken kids you've really got in mind, Peter.
The argument put forward by Hitchens and many others is perpetuated by an endless cycle - a large chunk of those in power and influence will always hanker after selection for the very simple reason that they benefitted from it themselves. Because they naturally have a self-image of having got to where they are today solely through their own endeavour, they imagine that the system that allowed them to do so must be the 'fairest'. But those whose lives were blighted by being shunted off to secondary moderns have - almost by definition - no voice with which to tell the other side of the story. If you want to know what really happens when you have "rigorous selection, solely on merit", you need look no further that the current undergraduate populations of Oxford and Cambridge, and see just how closely it matches up with the demographics of the general population.