Form D31a: Navigating HMRC's Compliance Framework for Non-Long-Term UK Residents

On 6 April 2025, the United Kingdom formally dismantled one of the most long-standing pillars of its international tax system: the concept of domicile as the primary determinant for offshore inheritance tax liability. In its place, HMRC inaugurated strictly residence-based frameworks: the Foreign Income and Gains (FIG) regime for income and capital gains tax, and a new long-term resident test for Inheritance Tax (IHT), generally defined as being resident in the UK in at least 10 of the previous 20 tax years. This transformation in the IHT landscape has introduced significant compliance mechanisms, centralized in the supplementary schedule Form D31a, officially titled "Tell HMRC about a transferor or settlor who is not a long-term UK resident".

This supplementary form represents a critical shift in the administrative duties of trustees, personal representatives, and high-net-worth individuals. Effective exclusively for inheritance tax chargeable events occurring on or after 6 April 2025, Form D31a serves as the dedicated portal through which taxpayers must detail the residency background of non-long-term UK resident transferors or settlors. Under no circumstances can this document be treated as an isolated filing: it must be submitted alongside a primary return from the IHT100 series.

The Legacy of Domicile vs. The Residency Regime

For generations, the UK tax code offered unique advantages to "non-domiciled" individuals (non-doms). By utilizing the remittance basis of taxation, wealthy international citizens residing in the UK could shield their foreign-sourced income and gains from UK taxation, provided those funds were not brought into the country. Similarly, offshore trusts established by non-domiciled settlors enjoyed robust protections from UK inheritance tax (IHT).

However, the legislative overhaul that reached fruition on 6 April 2025 fundamentally altered this landscape. The transition away from the subjective, hereditary concept of "domicile" toward an objective, year-count "residence" framework represents a profound structural evolution. To provide administrative clarity, HMRC has developed specific compliance guidance for the residence regime within its official manuals index. This guidance acts as the primary guiding text for tax inspectors and practitioners navigating the complex transitional rules.

Technical Specifications of Form D31a

Form D31a is explicitly designed to collect granular information regarding individuals who act as transferors or settlors in transactions triggering inheritance tax charges, but who do not meet the statutory definition of a "long-term UK resident" (defined as being a UK resident in at least 10 of the previous 20 tax years).

Crucially, the form applies only to transactions and events occurring on or after 6 April 2025. It cannot be applied retroactively to inheritance tax events that occurred prior to this date. Taxpayers must recognize that Form D31a is not a standalone tax return. Submitting it independently constitutes an invalid filing, which HMRC will reject. Instead, the form must always accompany a primary Inheritance Tax return from the IHT100 series (specifically forms IHT100a to IHT100h).

The Boundary of Confusable Instruments

To prevent filing errors, practitioners must understand the exact differences between Form D31a and other primary HMRC tax forms.

Form D31a must not be confused with Form IHT100 itself, as the latter is the substantive tax return while the former is merely a supportive residency schedule. Furthermore, Form D31a is legally distinct from Form IHT400. While the IHT100 series (supported by D31a) deals primarily with lifetime transfers and specific trust events, Form IHT400 is the comprehensive tax return filed to report a person's entire estate upon death.

The regulatory distinctions established by HMRC are outlined in the following table:

Software Compliance and Administrative Rigor

HMRC's digital infrastructure provides practical recommendations for completing Form D31a. As a technical compatibility recommendation, rather than a strict legal obligation of the taxpayer, HMRC suggests downloading the PDF form and saving it to a local computer, editing it using the latest free version of Adobe Reader. Attempting to complete or open the form directly within an internet browser often triggers compatibility errors or data corruption, leading to processing delays or administrative rejection due to IT issues.

Chronology of Updates

The regulatory lifecycle of this reporting schedule has progressed through clear milestones over the past months:

1. 6 April 2025: Initial publication of Form D31a alongside the formal commencement of the new UK residence-based tax regime.
2. Continuous Guidance: Ongoing publication and integration of compliance guidance for the regime within HMRC's official manuals index.
3. 24 September 2026: Update to Form D31a according to HMRC official records.

Practical Implications for Trustees and Advisors

Trustees of offshore structures and wealth planning advisors must immediately integrate Form D31a into their standard compliance checklists. Upon the occurrence of any lifetime chargeable event, such as a trust's ten-year anniversary charge or an exit charge, a rigorous analysis of the settlor's historical residency must be performed to determine if the D31a schedule is required, keeping in mind that Form D31a is only activated if the chargeable event exceeds exempt thresholds and mandatory reporting under the IHT100 series is triggered.

Failure to append Form D31a when reporting a transaction involving a non-long-term resident transferor will render the primary IHT100 return incomplete, exposing the trust and its trustees to administrative rejections and potential penalties. Technical precision in gathering historical residency data is therefore an indispensable element of UK inheritance tax compliance under the post-2025 regime.