Six days from now, the first UK Pillar Two filings are due. For accounting periods ending 31 December 2024, the deadline to submit a GloBE Information Return (or Overseas Return Notification) and a UK Self Assessment return to HMRC is 30 June 2026. If your group has consolidated revenues above €750 million and any UK presence at all, you are almost certainly in scope — and the penalty for missing this deadline is not trivial.
The problem I keep seeing is the assumption that Pillar Two is someone else’s problem. The parent company handles it. The group tax team is on top of it. There is no UK tax to pay, so there is nothing to file. All three of those assumptions can be wrong simultaneously, and HMRC will not be sympathetic.
What Pillar Two Actually Is — and What It Is Not
The OECD’s Pillar Two framework, adopted by the UK through the Finance (No.2) Act 2023 and subsequently Finance Act 2024, is a global minimum tax mechanism. The target rate is 15% effective tax rate in every jurisdiction a large group operates in. If any jurisdiction falls below that floor, top-up tax is collected — either in the UK or at the level of the ultimate parent.
Two separate UK taxes implement this. The Multinational Top-up Tax (MTT) applies to UK parent entities that have low-taxed profits sitting in overseas subsidiaries. The Domestic Top-up Tax (DTT) applies where UK profits themselves fall below 15% — something that can happen if a group has substantial UK capital allowances, R&D relief, or investment incentives that temporarily suppress the effective rate.
What matters for 30 June is not primarily whether you owe money. It is whether you have filed. And filing is mandatory for every in-scope group, regardless of whether the computation produces a liability.
The Threshold Test: Smaller Than You Think
The revenue threshold — €750 million consolidated annual revenue in at least two of the previous four accounting periods — is measured at group level, not UK entity level. A UK subsidiary with £20 million of revenue is fully in scope if its ultimate parent group clears €750 million globally. The size of the UK footprint is irrelevant to the question of scope; it only affects whether any top-up tax is actually due.
This is the trap. The UK entity’s local finance team sees a manageable P&L, assumes Pillar Two is a big-company problem, and takes no action. Meanwhile, the filing obligation is live and the clock is running. HMRC’s own guidance is unambiguous: groups with UK entities must register and file even if their UK presence is limited to a single branch.
What the 30 June Deadline Actually Requires
Two separate submissions are due by 30 June 2026 for groups with a 31 December 2024 year-end:
The GloBE Information Return (GIR) or Overseas Return Notification (ORN). The GIR is the detailed global computation — effective tax rates by jurisdiction, top-up tax calculations, safe harbour elections, and allocation of any liability. Most non-UK-headed groups will not file the GIR directly in the UK. Instead, it is filed centrally by the ultimate parent in its home jurisdiction, and the UK filing member submits an ORN to HMRC confirming where it was filed. The ORN must identify the filing jurisdiction, the filing entity, and the date of submission. Getting this wrong — or not doing it at all — creates an immediate compliance failure.
The UK Self Assessment return. This is a standalone statutory filing, completely separate from the standard CT600. It covers both MTT and DTT, states the UK group’s liability (which may be nil), and allocates any liability across UK members. Every registered group must submit this return. An ORN does not substitute for it. Nil returns are still returns.
One further complication: neither the GIR nor the Self Assessment return can be submitted using standard corporation tax software. HMRC’s Pillar Two reporting service is a separate digital platform, and the GIR requires specialist third-party software that can handle the underlying data architecture and HMRC’s technical submission format. Groups that assumed their existing tax compliance team could handle this with existing tools are discovering, at the last minute, that they cannot.
The Safe Harbours That Could Save You Significant Work
Before finalising the GloBE computation, every CFO should be asking whether transitional safe harbours apply. The most important for the June 2026 filing cycle is the Transitional Country-by-Country Reporting Safe Harbour (TCSH).
Under the TCSH, a group can use simplified data from its existing Country-by-Country Report to demonstrate that it passes one of three tests in a jurisdiction: a de minimis revenue and profit test, a simplified ETR test of at least 17% (15% for certain years), or a routine profits test. If a jurisdiction passes, the top-up tax for that jurisdiction is deemed to be nil. The TCSH has been extended and now applies to fiscal years beginning before 1 January 2028 — meaning it is available for both the FY2024 and FY2025 filing cycles for calendar-year groups.
The UTPR Safe Harbour is less immediately relevant — the UK’s Undertaxed Profits Rule does not come into force until accounting periods beginning on or after 31 December 2024 (i.e., FY2025 filings, due June 2027). But groups whose ultimate parent is in a jurisdiction with a corporate tax rate of at least 20% should be modelling now whether they will qualify. The first MTT cycle is in many ways the rehearsal for the UTPR, which is the rule with the most complex cross-jurisdictional implications.
If you have not yet assessed your safe harbour position, the OECD’s Safe Harbours and Penalty Relief guidance is the starting point, alongside the June 2024 Agreed Administrative Guidance from the Inclusive Framework.
The UTPR: Why You Need to Be Thinking About FY2025 Now
The June 2026 filing covers FY2024 — a period in which the UK’s IIR (MTT) applied but the UTPR did not. The first UTPR filing will be June 2027, covering FY2025. That sounds distant enough to park, but it is not.
The UTPR is the backstop mechanism in the GloBE architecture. Where a low-taxed group entity is not picked up by the primary IIR — because the ultimate parent is in a jurisdiction that has not implemented Pillar Two — the UTPR allows other jurisdictions to collect the residual top-up tax. The UK will do exactly that from FY2025 onwards. Allocation is based on a 50/50 split between employees and tangible assets in the collecting jurisdiction, so groups with a meaningful UK headcount or asset base will want to model their exposure before the end of the current calendar year.
One development worth watching closely: the G7 “Side-by-Side” agreement from June 2025 carved out exemptions from IIR and UTPR for US-parented groups under certain conditions. For UK groups with US operations or a US ultimate parent, the interaction between this carve-out and the UK UTPR is technically complex and genuinely unresolved in parts. If this describes your group structure, get a specialist opinion now rather than in April 2027.
Registration: Did You Miss the First Deadline?
Groups that came into scope for FY2024 (year-end 31 December 2024) were required to register with HMRC by 30 June 2025 — 18 months is the window, but registration must happen no later than 6 months after the end of the first in-scope period. If your group has not yet registered, the Pillar Two digital service is still open, but you are already in breach of the registration timeline and should take advice on the penalty position.
Registration is straightforward in principle — you need the ultimate parent entity details, the filing member details, accounting period dates, and contact information for the responsible tax team. You will receive a Pillar Two reference number on completion. Print that page; HMRC does not send a confirmation email. The registration is a one-off, not an annual requirement.
Six CFO Actions Before 30 June 2026
1. Confirm in-scope status immediately. Run the revenue threshold test at group level using consolidated financial statements. If you are in scope and have not yet registered, do so today. The penalty framework under Schedule 41 Finance Act 2008 applies from day one of non-registration.
2. Identify your filing member and confirm GIR jurisdiction. For non-UK-headed groups, the GIR is almost certainly being filed elsewhere. Confirm with your group tax team exactly where it has been or will be filed, by whom, and on what date. The ORN you submit to HMRC must contain this information accurately.
3. Verify your specialist software is live and tested. Standard CT600 software does not work for Pillar Two Self Assessment returns. If your tax compliance team does not already have access to a working solution, escalate today. HMRC will not grant informal extensions because the software was not procured in time.
4. Apply transitional safe harbours where applicable. Run the TCSH analysis against your CbCR data for every jurisdiction. If the test is met, document the election properly. Safe harbour claims need to be supportable and consistently applied. Do not assume they automatically apply without the documented analysis.
5. Prepare a nil-return even if you owe nothing. A nil UK Self Assessment return is still a statutory filing. It confirms that the in-scope group has considered the MTT and DTT position and that no liability arises. Missing it because “there is nothing to pay” is the most avoidable Pillar Two compliance failure there is.
6. Start modelling UTPR exposure for FY2025. The June 2027 deadline will arrive faster than expected, and the UTPR computation is materially more complex than the IIR. The data you collect now — substance footprint, employees by jurisdiction, tangible asset values — will be the foundation of that filing. Use the current compliance cycle to build the infrastructure for the next one.
The Broader Picture
Pillar Two is the most significant structural change to international corporate tax since the original transfer pricing framework. The 30 June 2026 deadline is the UK’s first live proof that the OECD’s grand bargain — coordinated global minimum tax in exchange for reduced unilateral digital services taxes — actually works in practice. HMRC is watching closely, and the penalty regime is designed to have teeth.
For CFOs of large UK subsidiaries, this is not an abstract group tax matter. You are personally responsible for your UK entity’s compliance. If the ultimate parent’s group tax team is not keeping you informed of your local filing obligations, you need to ask more direct questions. The ORN, the Self Assessment return, the registration — these are UK statutory obligations that sit with the UK filing member, not with a tax team in Luxembourg or Delaware.
The advisory community is clear: the most common Pillar Two compliance failures in the first filing cycle will be groups that assumed someone else had it covered. Make sure that is not you.