Not sure why you're getting downvoted because you are correct: London salaries are pitiful even before you factor in the enormous cost of living there (I lived and worked in London for 4 years but did contracting as the salaries even 10+ years ago were and are a joke comparatively).
It's one reason I and many others work in the US instead.
No idea what Brexit will do to relative incomes. It depends on what happens with the pound, what the visa situation looks like and so on.