Question to the Home Office:

To ask the Secretary of State for the Home Department, how many nationals of the United States are domiciled in the UK; and how many of those nationals have received visas to work (a) in the banking sector and (b) elsewhere in the financial services sector.

The Home Office does not hold data on the number of US nationals who are
domiciled in the UK. The concept of domicile is not linked exclusively to a
person’s immigration status, nor does the fact that a person is deemed to have
domicile in the UK necessarily mean that they are currently present in the UK.

Information on those domiciled in the UK is a matter for HM Revenue and Customs
https://www.gov.uk/tax-foreign-income/non-domiciled-residents