Making GBP 150,000 before tax in the year 2019-2020 would put a person in the 98th percentile of salaries in the UK. If that's not rich, I don't know what is, in London or anywhere.
Rich refers to wealth, not income. Having a high income does not mean that one is rich, and it will take a very long time to get rich on 150'000 in London - assuming you live modestly and are able to sustain that level of income for a long time.