Selection is not "discrimination", please refer to the relevant laws. You can invent whatever you want, but this won't change the reality.
Yes, children should have access to education and the solution would be opening grammar schools everywhere, not closing them everywhere as in your "universe". Of course the gov is not going to open more grammars, they don't need clever people so there is nothing to discuss here.
Too many people, like yourself, think that dragging everyone down is good, and that's a massive problem. Britain has been behind for ages on so many STEM things, from space missions to shipbuilding to whatnot. The chaos with education (not current VAT but general inability of successive governments to improve anything) will only exacerbate this problem. You cannot have rocket science (any "rocket science") if your population is so uneducated that people can't do basic maths. "Socialists" can shout equality slogans from the rooftops 24x7 till their throats are coarse - this won't make children literate and numerate and STEM advanced to the highest standard that is required now.
Banning grammars or any selection won't make the comps better - it's not about mixing everyone together, it's about the cultural values and motivation. If people are shouting "we don't need no education" - they can be MC, WC or posh, the results will be miserable. If people are fantasising "oh let's try one crazy policy, if it doesn't work - we'll do the next crazy one" - the results will be disastrous. Birbalsingh is not "experimenting on children" like the government after government have been doing, and she's not mixing "rich" with "poor" as the "rich" stay away, but her school gets excellent results with a very poor and disadvantaged intake - just because her teaching approach, methods, demands, motivation and enforcement make children learn. And I repeat - LEARN, not faff about constantly measuring if everyone is "perfectly equally equal", and whether one is doing better than the other, and planning how to drag your classmate down. She's creating the race to the top and no wonder she is being hated by the lefties.
So yes, rest assured, the population will remain largely illiterate and the elites will have no problem to rule the people.