My brother lives in crouch end (North London, about 30 mins cycle from Westminster for those that don't know where it is).
Best fixed line speed available to him? 6mb.
In the 80s two houses were demolished and a small block of flats put up (think there are 12 flats in the block), so BT put direct connections to the flats from a nearby exchange. So, no cabinet to get fttc from, and the exchange is far enough away that adsl is slow. Although there is cable in the street, it doesn't run to the block and virgin aren't interested in installing it even though most in the block want it. 12 is too few to bother apparently. Even 5G isn't good, as the transmitter is blocked by a small hill and many many buildings. Best connection I found him was 20mb ish on 4G.
Open Reach haven't even published when they are going to put fttp in the road, so I expect at least a decade before he can get anything better.