I wish that countries would mandate symmetrical connections as well. This would open up so much more opportunity for self hosting web apps and allow for decentralized sites, such as peertube, to function better.
I disagree. The vast majority of people are never going to need or care about hosting a decentralized hoozywhatsit. Mandating technical decisions that cause waste is suboptimal. You get symmetrical speeds with fiber, but if ISPs could use the existing fiber infrastructure and allocate 75% of the bandwidth as download instead of 50%, that would be a win.
That depends on the fiber access mechanism. GPON is usually 2.4 G down / 1.2 G up TDMA over a shared medium. The downstream direction has perfect synchronization because it's a single sender, but upstream synchronization is more difficult across the many terminals, so they use a lower speed to compensate. I don't know what the common fiber connectivity models are in the UK though.