This explains part of it. Lots of cashed up people.
The IFS said it took an income of about £100,000 to be considered among the top 1% of high earners in Wales, the north-east and Northern Ireland. However, in London it was more than £300,000 a year.
In a sign of the extreme levels of wealth in the capital, it said a 50-year-old man in London with an income of £160,000 would earn enough to be in the top 1% for the rest of the country, but would not even be in the top 5% of men living in London.
From here https://amp.theguardian.com/business/2019/aug/06/london-is-increasingly-home-to-the-top-1-by-income-study-finds