I lived in a borough of London and was unable to get anything more than 1.7MB/s down and 100KB/s up without paying for FTTP...this was in an apartment block with ~20 apartments, sort of a new build
We're using 3s new 5g service and it's £25/month (2 year contract) for what they claim is 400mb/s download speed, although in practice it fluctuates a lot but is always > 100mb/s.