UK Draft Law Implements OECD Pillar Two Side-by-Side Package for US-Parented Groups

On 13 July 2026 the UK published draft Finance Bill 2026-27 legislation implementing the OECD's January 2026 Side-by-Side Pillar Two package. The measures introduce permanent and extended safe harbours, qualifying tax incentive rules, and the Side-by-Side Safe Harbour that materially alters how US-parented multinational groups calculate UK top-up tax.

Several provisions apply retrospectively to accounting periods beginning on or after 1 January 2026 — weeks after HMRC told Parliament's Public Accounts Committee that the US exemption from Pillar 2 would cut expected UK receipts by £600 million a year. The draft law gives legislative form to that policy shift.

For qualifying groups, the Side-by-Side Safe Harbour switches off UK Multinational Top-up Tax under both the Income Inclusion Rule and Undertaxed Profits Rule from periods beginning on or after 1 January 2026. UK Domestic Top-up Tax and foreign qualified domestic minimum top-up taxes remain in force.

The Ultimate Parent Entity Safe Harbour similarly switches off UTPR exposure for the UPE jurisdiction. Together these measures implement the OECD package the UK confirmed on 7 January 2026 via ministerial statement HCWS1224.

The government stresses draft legislation is not yet enacted and final Finance Bill contents remain subject to the Chancellor's decision — but groups should model positions on the published text now.

The permanent Simplified ETR Safe Harbour deems jurisdictional top-up amounts nil where a simplified effective tax rate reaches at least 15%. The calculation modifies standard GloBE ETR rules across revaluations, hybrid entities, permanent establishments, deferred tax, and intragroup transactions — requiring separate annual elections for subgroups within a territory.

A 24-month look-back prevents groups toggling between simplified and full calculations where a jurisdiction recently generated top-up tax. Early access is available for calendar-2026 periods where QDMTT safe harbour is elected, only one jurisdiction has Pillar Two taxing rights, or equivalent elections are made in every relevant IIR jurisdiction.

The Transitional CbCR Safe Harbour extends by one year for periods beginning by 31 December 2027 and ending by 30 June 2029 — giving groups additional breathing room while GloBE systems mature.

New qualifying tax incentive rules adjust covered taxes and, where relevant, adjusted profits for expenditure- and production-based incentives from periods beginning on or after 1 January 2026. Most other technical amendments to multinational and domestic top-up tax take effect from 31 December 2026.

Irish in-scope groups filed initial Pillar Two returns by 30 June 2026 through ROS. The UK Side-by-Side package does not remove Irish qualified domestic top-up tax obligations — but it reshapes where US-parented groups pay UK top-up amounts relative to Irish constituent entities.

Technical consultation on the draft Schedule closes 7 September 2026 alongside the wider Finance Bill package.

US-parented groups should rerun Pillar Two models under Side-by-Side Safe Harbour elections, comparing results against the £600 million annual receipt shortfall HMRC disclosed to the PAC on 10 July 2026.

Document safe harbour elections, simplified ETR working papers, and subgroup analysis before HMRC enquiry — the PAC simultaneously warned that £21 billion of large-business tax under consideration relates to international profit-shifting risk.

FinnAccountings tracks Pillar Two filing deadlines and safe harbour elections across UK and Irish entities — start a free trial to keep multinational minimum tax compliance aligned as Finance Bill 2026-27 moves toward enactment.