The basic, higher and additional Income Tax rates, the band boundaries they apply to, and the Personal Allowance taper above £100,000.
Primary source: Income Tax rates and allowances (GOV.UK).
Income Tax is charged on taxable income above the Personal Allowance. The allowance is set against income first, and the remainder is then taxed in bands: the basic rate on the first band, the higher rate on the next, and the additional rate on anything above that.
The bands are marginal, not flat. A taxpayer whose income crosses a band boundary pays the lower rate on the portion below the boundary and the higher rate only on the portion above it, so the rate that applies to the last pound of income is not the rate that applies to all of it.
The standard Personal Allowance is reduced where income exceeds £100,000. For every £2 of income above that threshold, £1 of allowance is withdrawn, so the allowance is exhausted at £125,140. The effect is a higher effective marginal rate on income in that range, because each additional pound both attracts tax and withdraws allowance.
The basic, higher and additional rates and the band boundaries they apply to are published for each tax year separately. The Tax Rulebook keeps the 2024–25, 2025–26 and 2026–27 editions side by side, so a rate that has changed can be read against the year it applied to.