Although you could, if you have passed the minimum contract term, migrate your FTTC to someone who doesn't cap Fibre 1 service. An example of an ISP that provides this is Zen, there are probably others.
If you have Fibre 2 from Zen (at 78Mbps) then they state that their own infrastructure guarantees 40Mbps throughput, although it can be higher if there is spare capacity. Zen has PoPs all over the UK so they take their customers' backhaul data out of the BT network as early as they can. In my case this is at the main exchange in the area which is a few miles away, the fibre to my cabinet doesn't go anywhere near my actual exchange with the twisted pair copper line.