HMRC Advance Tax Certainty Service 2026 and GAAR Advisory Opinion: What UK Tax Professionals Need to Know

Introduction: Two Major UK Tax Developments in 2026

The UK tax landscape is evolving rapidly in 2026, with two significant developments that demand immediate attention from tax professionals and businesses. First, HM Revenue & Customs (HMRC) is launching its Advance Tax Certainty Service on 1 July 2026, a game-changer for large-scale investors seeking binding clarity on complex tax treatments. Second, the GAAR Advisory Panel has issued a critical opinion on 30 January 2026 targeting inheritance tax (IHT) avoidance schemes involving share acquisitions and employee trusts. These developments reinforce HMRC's commitment to transparency and anti-avoidance, making UK tax compliance 2026 a pivotal year for proactive planning.

This article breaks down both updates, explains their implications, and provides practical steps for tax professionals—including tax agent registration requirements—to stay ahead.

HMRC Advance Tax Certainty Service: Binding Clarity for Major Investments

What Is the Advance Tax Certainty Service?

Announced by HMRC, the Advance Tax Certainty Service is a new facility that allows businesses to obtain binding clearances on how UK tax rules apply to major investment projects before final investment decisions are made. The service launches on 1 July 2026, with expressions of interest accepted from 1 June 2026. HMRC aims to issue clearances within 90 days of receiving a formal submission.

Eligibility and Scope

To qualify, projects must involve at least £1 billion of qualifying expenditure in the UK. The service covers:

• Corporation Tax
• VAT
• Stamp Duty Land Tax
• Income Tax
• PAYE
• Construction Industry Scheme

Notably, transfer pricing is excluded. The clearance is binding on HMRC, providing certainty that encourages long-term investment and supports economic growth.

Why This Matters for UK Tax Compliance 2026

For businesses undertaking large infrastructure, technology, or energy projects, tax uncertainty can delay or derail investment. The Advance Tax Certainty Service reduces that risk, enabling companies to proceed with confidence. Tax professionals advising on such projects should prepare to submit expressions of interest from June 2026 and ensure their clients meet the £1 billion threshold.

GAAR Advisory Panel Opinion: Targeting Inheritance Tax Avoidance

Background of the Opinion

On 30 January 2026, the GAAR Advisory Panel published an opinion on arrangements designed to reduce the value of an estate for Inheritance Tax (IHT) and avoid IHT on a lifetime transfer. The scheme involved acquiring shares in a company and then gifting those shares to an employee trust. The Panel concluded that entering into and carrying out such arrangements is not a reasonable course of action in relation to the relevant tax provisions—meaning these arrangements are considered abusive tax avoidance.

Implications for Inheritance Tax Avoidance Schemes

This opinion serves as a clear warning: HMRC is actively scrutinising IHT planning that uses trusts and share transfers. Tax professionals must review any existing or planned structures involving employee trusts and share acquisitions. If the GAAR applies, HMRC can counteract the tax advantages, potentially leading to significant additional tax liabilities, penalties, and interest.

The GAAR Advisory Panel opinion includes detailed documents (PR1, PR2, PR3, Trustee) that provide reasoning. Advisers should study these to understand the boundaries of acceptable planning.

Practical Steps for Tax Professionals

1. Register as a Tax Agent with HMRC

Professional tax agents in the UK must register with HMRC as a legal requirement. The process involves:

• Creating an Agent Services Account or an HMRC Online Services Account.
• Obtaining agent codes for specific tax services (e.g., Self Assessment, VAT, PAYE, Corporation Tax).
• Enrolling in the relevant services and obtaining client authorisation before acting on their behalf.

Registration is being introduced in stages based on circumstances. Updated guidance was published in May 2026, so agents should verify they are compliant with the latest requirements. Early registration ensures seamless access to the Advance Tax Certainty Service and other HMRC digital tools.

2. Prepare Clients for the Advance Tax Certainty Service

For clients with large-scale UK investments, start discussions now. Identify projects with qualifying expenditure of £1 billion or more. Gather detailed information on the proposed transactions, including corporate structure, financing, and expected tax treatments. Expressions of interest open on 1 June 2026, so be ready to submit promptly.

3. Review IHT Planning Arrangements

Given the GAAR opinion, review any existing or proposed IHT schemes involving share acquisitions and employee trusts. If the arrangements resemble those described in the opinion, consider restructuring or seeking alternative planning that falls within acceptable boundaries. Document the commercial rationale to demonstrate that the arrangement is not abusive.

Key Takeaways

• HMRC Advance Tax Certainty Service launches 1 July 2026; expressions of interest from 1 June 2026. Eligible projects: £1 billion+ qualifying expenditure. Binding clearance within 90 days.
• GAAR Advisory Panel opinion (30 January 2026) confirms that IHT avoidance via share acquisition and gifting to employee trusts is abusive and not reasonable.
• Tax agent registration is mandatory for paid tax advisers. Create an Agent Services Account and obtain necessary codes.
• Proactive compliance is essential: prepare for the new service and review IHT planning to avoid GAAR challenges.

Stay Ahead with Multi-Domain Compliance Tracking

Navigating these UK tax updates alongside evolving regulations in AI governance, cybersecurity, ESG, and other domains can be overwhelming. AIGovHub provides a centralised platform for tracking regulatory changes, assessing compliance gaps, and managing risk across multiple jurisdictions. Explore AIGovHub's compliance tools to streamline your UK tax compliance 2026 and beyond.

This content is for informational purposes only and does not constitute legal advice.