In all practicality, those enjoying faster speeds will continue to enjoy them, while everyone else will get boosted to 100Mb.
I wouldn't want to assume anything as good as that ! Given Corbyn's fluffy thinking, the idea of a state-determined speed "and that's what you get" is not off the cards. lets face it, the idea that someone with a bit more brass can buy something better than the poor old chap earning a pittance down t'mine would be an anathema to a hardline socialist like him. Not that he seems averse to enjoying the fruits of his generous MP's salary and having the generous state funded MP's pension to look forward to.
Elsewhere I read a good suggestion. You superglue a load of climate protesters to the outside of your your building for insulation. Install a Boris for constant hot air heating. Put a Farage in the basement for a constant supply of manure for the methane digester. And finally, put a Corbyn in the loft for wooly insulation from the harsh reality of outside.