All these sort of sites sufer from the problem that those publishing their data are self selecting
So they do it because either their speeds are the best or they are the worst.
The majority who are happy are not going to be running test/publishing data.
What you actually need for a proper analysis is the OFCOM sync speed dataset of max,median and average speeds for EACH post code in the UK.
(Post codes with too few houses on are listed as "insufficient data")
Here we are - it's is a mega 11MB+ csv file once unzipped and some programs may not be able to open it
On this page....http://maps.ofcom.org.uk/broadband/