What happened?
Budget 2026 confirms planned Finance Bill 2026–27 amendments to UK Multinational Top-up Tax and Domestic Top-up Tax. HMRC’s policy paper, updated on 28 October 2026, sets out the operative dates and scope of further technical changes. The package had previously been announced; the practical focus is its differentiated timing and elections.
Key details
The proposals include Side-by-Side and ultimate-parent-entity safe harbours, a substance-based tax incentive safe harbour, a simplified effective-tax-rate safe harbour and extension of the transitional safe harbour. Further amendments address cross-border covered-tax allocation, post-filing adjustments, investment entities and permanent establishments.
Who is affected?
Multinational groups within the UK top-up-tax regimes should review their UK computations alongside group-wide Pillar Two positions. A safe-harbour proposal does not establish automatic eligibility for every group or remove all domestic top-up-tax obligations.
Effective date / timing
The Side-by-Side package is intended for accounting periods beginning on or after 1 January 2026. Most other technical amendments have a default start for periods beginning on or after 31 December 2026, with earlier application available by election for many changes. The transitional UTPR safe-harbour adjustments for 52- or 53-week periods are intended from periods beginning on or after 31 December 2024. Certain typographical amendments apply from periods beginning on or after 31 December 2023. These are proposed legislative application dates, not confirmation of enactment.