Levels.fyi is always very inflated for anything outside of FAANG – to the point where it's not realistic
Glassdoor lists the average for SWEs for Madrid at 35k€ vs London at £66k (76k€) which even accounting for cost of living is quite a big difference
But be aware that the London salaries upper tail is wider, possibly brought up by the quant firms (which are a different kind of company than most are accustomed)
levels.fyi gives 112kE as the median and 200kE/90% for London vs around 60kE for the median and 90kE/90% (pretax for both)