HMRC’s Income Tax liabilities statistics publish a breakdown of the number of individual Income Tax payers by marginal rate in Table 2.1. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1165820/govuk_table2_1_.xlsx These figures are based on the 2019 to 2020 survey of personal incomes, projected in line with Office for Budget Responsibility (OBR) economic determinants.