It goes back over a decade when there were some high profile dodgy clinics that consistently churned out bad results. The unfortunate patients would turn to the forums for help, the bad work was seen worldwide and unfortunately some mud sticks. The bad work made a lasting impression.
The people who make these claims now can`t possibly know the quality of every UK clinic. Have they the time to scrutinise every website? I think not. The same people will probably watch a few Youtube videos of cherry picked patients and then name these clinics as the best etc etc. The internet is a great resource but it`s also a means of spoon feeding people information.
The UK pricing is very similar to most Western countries, the US and Canada. Obviously, countries with lower living costs and overheads are able to charge less.