UK income tax starts after the personal allowance (£12,570 for most), then 20% on the basic-rate band, 40% above roughly £50,270, and 45% on the additional-rate band.
National Insurance is separate and has its own thresholds, so your marginal deduction at a given salary is income tax plus NI combined — often higher than people expect around the higher-rate boundary.
The allowance tapers away above £100,000 (£1 lost for every £2 earned), creating an effective 60% band — a quirk worth modelling before taking a raise or bonus into that range.
Try it: UKMoneyCalc on uk take home pay.