英国遗产税对秘密信托的承认：遗嘱中未公开受益人的安排

The UK’s inheritance tax (IHT) framework has long grappled with arrangements that deliberately obscure the true beneficiaries of an estate. Among the most legally intricate of these is the secret trust—a mechanism where a testator leaves assets to a person in their will who appears to be the outright beneficiary, but who is in fact holding those assets on trust for an undisclosed third party. These trusts are fully recognised in English law, yet their interaction with HMRC and the IHT regime creates significant compliance risks. According to HMRC’s 2023-24 annual inheritance tax statistics, total IHT receipts reached £7.5 billion, a 4.2% increase from the previous year, while the Office for Budget Responsibility (OBR) projects receipts will rise to £9.5 billion by 2028-29. As the scope of IHT widens—with frozen nil-rate bands and rising asset values—the use of secret trusts by families seeking privacy or planning for non-traditional relationships is under renewed scrutiny. This article examines how UK inheritance tax law treats secret trusts, the disclosure obligations of trustees, and the practical risks for executors who administer estates containing unrevealed beneficiary arrangements.

The Legal Foundation of Secret Trusts in English Succession Law

A secret trust arises when a testator makes a will that leaves property to a named individual (the “secret trustee”) on the understanding—communicated during the testator’s lifetime—that the property will be held for an undisclosed beneficiary. English courts have upheld these arrangements for over three centuries, treating them as operating outside the will itself to avoid the strict formalities of the Wills Act 1837. The key legal principle is that secret trusts are enforced not because of the will’s wording, but because equity will not allow a statute to be used as an instrument of fraud. If the secret trustee were permitted to keep the property for themselves, that would constitute fraud on the testator’s true intentions.

There are two recognised categories: fully secret trusts, where the will makes no mention of any trust at all, and half-secret trusts, where the will indicates the property is given on trust but does not name the beneficiary. In a fully secret trust, the will simply gifts the asset to the trustee outright; in a half-secret trust, the will states “to X on trust” but omits the beneficiary’s identity. The distinction matters for IHT purposes because the timing of the communication and the trustee’s acceptance differ. For a fully secret trust, the communication must occur before or at the time the will is executed; for a half-secret trust, it must occur before execution and the will must incorporate the trust by reference. Failure to meet these requirements can render the trust void, leaving the property to pass under the will’s residuary clause—potentially triggering unintended IHT consequences.

The “Three Certainties” Requirement

For any secret trust to be valid, it must satisfy the three certainties of English trust law: certainty of intention, certainty of subject matter, and certainty of objects. The certainty of objects is particularly challenging in secret trusts because the beneficiary’s identity is not recorded in the will. The testator must have communicated the beneficiary’s identity to the secret trustee during their lifetime, and the trustee must have accepted the obligation. If the beneficiary is described vaguely—for example, “my old friend”—the trust may fail for uncertainty, and the property reverts to the residuary estate. HMRC may then assess IHT on the basis that no valid trust existed, treating the gift as a failed disposition and applying the standard 40% rate on any value exceeding the nil-rate band.

How HMRC Treats Secret Trusts for IHT Purposes

HMRC’s approach to secret trusts is governed by the principle that substance prevails over form. For IHT purposes, the relevant property is treated as belonging to the beneficial owner, not the apparent legal owner under the will. This means that when a testator dies, the assets held on a valid secret trust are not part of the secret trustee’s estate for IHT purposes—they are treated as passing directly to the undisclosed beneficiary. However, this creates a critical compliance gap: the executors who submit the IHT account (form IHT400) must know about the trust to report it correctly. If the secret trust is truly secret—known only to the testator and the secret trustee—the executors may file the account showing the property as passing to the named beneficiary, potentially understating or overstating the IHT liability.

The IHT treatment depends on the nature of the trust. A secret trust is typically a bare trust for IHT purposes, meaning the undisclosed beneficiary has an immediate right to the capital and income. On the testator’s death, the property is treated as a transfer of value to that beneficiary, and any IHT due is calculated based on the beneficiary’s relationship to the testator and the availability of the nil-rate band (£325,000 as of the 2024-25 tax year, frozen until 2028). If the undisclosed beneficiary is a spouse or civil partner, the transfer is wholly exempt under the spouse exemption. If the beneficiary is a child or other relative, the standard IHT rates apply. The secret trustee’s own estate is not liable for IHT on those assets, but the trustee may have a duty to report the trust to HMRC if they receive income or capital gains.

Disclosure Obligations and Penalty Risks

The secret trustee faces a significant dilemma: they must disclose the trust to HMRC to avoid penalties, but doing so may reveal the arrangement to other family members or defeat the testator’s purpose of secrecy. Under the Trust Registration Service (TRS), which HMRC introduced in 2017 and expanded in 2022, most UK trusts must register their beneficial ownership details, including the identity of the undisclosed beneficiary. Failure to register a registrable trust can result in penalties of up to £5,000 plus daily fines. However, secret trusts that arise on death and are wound up within two years may be exempt from registration if no ongoing trust exists. This narrow window creates a practical challenge: the secret trustee must decide quickly whether to register or distribute, and any delay risks HMRC scrutiny.

Case Studies: Mrs X and Mr Y

Mrs X: A Fully Secret Trust for a Non-Marital Partner

Mrs X, a widow aged 78, executed a will in 2019 leaving her entire estate—valued at £1.2 million, including a London flat worth £850,000—to her neighbour, Mr A. What the will did not disclose was that Mrs X and Mr A had agreed orally that Mr A would hold the flat on trust for Mrs X’s long-term companion, Miss B, who was not a relative and whom Mrs X did not wish to name in the will for family privacy reasons. Mrs X died in 2023. Mr A, as executor and secret trustee, filed the IHT400 showing the estate passing to himself as sole beneficiary. He claimed the full nil-rate band and residence nil-rate band (£175,000 for 2023-24), reducing the taxable estate to £700,000 and IHT to £280,000. However, HMRC later discovered the secret trust during a random compliance check. The correct IHT treatment required treating the flat as passing to Miss B, who was unrelated to Mrs X, meaning no spouse exemption applied. The residence nil-rate band was also unavailable because Miss B was not a direct descendant. HMRC reassessed the IHT at £340,000, plus a penalty of £68,000 for incorrect filing. Mr A was personally liable for the penalty as the reporting executor.

Mr Y: A Half-Secret Trust for Charitable Purposes

Mr Y, a retired solicitor aged 85, executed a will in 2021 that left £500,000 to his solicitor, Ms C, “on trust for purposes I have communicated to her.” The will did not name the beneficiaries. Mr Y had privately instructed Ms C to hold the funds for two small charities that he supported during his lifetime but did not wish to publicise. Mr Y died in 2024. The IHT treatment was straightforward: charitable gifts are exempt from IHT under section 23 of the Inheritance Tax Act 1984. Ms C applied for probate and filed the IHT400 showing the £500,000 as a charitable transfer, with zero IHT due on that portion. HMRC accepted the filing without further enquiry because the will explicitly referenced a trust, and Ms C provided the charity registration numbers upon request. This case illustrates that half-secret trusts for exempt beneficiaries can be relatively low-risk, provided the trustee is prepared to disclose the beneficiary details to HMRC if challenged.

Practical Risks for Executors and Trustees

Executors who administer an estate containing a secret trust face personal liability for incorrect IHT returns. If the executor files an IHT400 that does not reflect the true beneficial ownership—for example, by treating the secret trustee as the outright beneficiary—the executor may be liable for any additional IHT, interest, and penalties that arise from HMRC’s subsequent discovery. This liability exists even if the executor was unaware of the secret trust, unless they can demonstrate that they took reasonable steps to inquire about the estate’s arrangements. The risk is heightened when the secret trustee is also the executor, as in the Mrs X case, because the conflict of interest may be apparent.

Another practical risk involves the interaction with the probate registry. When applying for a grant of probate, executors must swear an oath that the information in the will is true to the best of their knowledge. If a secret trust exists, the will’s text is literally true—it does gift the property to the named person—but the oath may be misleading if the executor knows the property is not for that person’s benefit. The probate registry does not routinely investigate secret trusts, but if a dispute arises later, the executor’s oath could be challenged as a misrepresentation, potentially delaying the grant or exposing the executor to contempt proceedings.

The Two-Year Winding-Up Window

Section 144 of the Inheritance Tax Act 1984 provides that if property is held on trust and the trustees appoint it to beneficiaries within two years of the testator’s death, the IHT treatment is generally the same as if the will had directly given the property to those beneficiaries. This two-year window is particularly useful for secret trusts, as it allows the secret trustee to distribute the assets to the undisclosed beneficiary without triggering additional IHT charges. However, the window does not apply if the trust is not properly constituted or if the distribution is part of a scheme to avoid IHT. For cross-border estates where beneficiaries are overseas, some families use channels like Airwallex global account to manage multi-currency distributions efficiently. Executors must document the distribution carefully to satisfy HMRC that the two-year rule has been met.

Disclosure Strategies and Compliance Options

Given the legal recognition of secret trusts but the strict IHT reporting requirements, practitioners have developed several disclosure strategies that balance the testator’s desire for privacy with HMRC compliance. The most common approach is to include a “letter of wishes” that is held separately from the will but referenced in a codicil. While a letter of wishes is not legally binding in the same way as a trust deed, it provides evidence of the testator’s intentions and can be shown to HMRC if challenged. For half-secret trusts, the will itself should clearly state that the property is held on trust, even if the beneficiary is not named, to avoid the risk of the trust being treated as a failed gift.

Another strategy is to use a life interest trust within the will, where the named beneficiary has a right to income but not capital, and the remainderman is undisclosed. This structure is more transparent to HMRC because the will acknowledges a trust, but the ultimate beneficiary remains private. The IHT treatment is governed by the relevant property regime, with periodic charges at 6% on the trust value every ten years. For estates valued above £2 million, the residence nil-rate band is tapered, making this structure less attractive for high-value properties.

Registration Under the Trust Registration Service

Since October 2022, the TRS requires all UK trusts with tax liabilities to register, including secret trusts that generate income or capital gains. The registration deadline is 90 days from the date the trust becomes liable to tax. For a secret trust that arises on death and is wound up within two years, registration may not be required if no ongoing tax liability exists. However, if the trust holds income-generating assets—such as rental property or dividend-paying shares—during the winding-up period, the trustee must register and report the trust’s beneficial ownership to HMRC. Failure to do so can result in penalties, and HMRC may share the information with other beneficiaries under the register’s transparency provisions. This creates a fundamental tension: the testator’s desire for secrecy may be undermined by the registration requirement.

FAQ

Q1: Can a secret trust be created orally, or does it need to be in writing?

A secret trust can be created orally, provided the testator communicates the trust terms to the secret trustee during their lifetime and the trustee accepts the obligation. However, oral trusts carry significant evidential risks. If the secret trustee dies before the testator, or if a dispute arises after the testator’s death, the court may require clear and convincing evidence of the arrangement. In Re Keen [1937], the Court of Appeal held that for a half-secret trust, the communication must occur before the will is executed. For a fully secret trust, communication can occur after execution but before death. HMRC will typically require written evidence—such as a letter or email—to accept the trust for IHT purposes. Without it, the property may be treated as passing to the named beneficiary, potentially triggering IHT at 40% on the full value.

Q2: Does the residence nil-rate band apply to a secret trust beneficiary who is not a direct descendant?

No. The residence nil-rate band (RNRB) is only available when the property passes to a direct descendant—defined as a child, grandchild, step-child, or adopted child. If the undisclosed beneficiary of a secret trust is a sibling, friend, or non-marital partner, the RNRB does not apply. For the 2024-25 tax year, the RNRB is £175,000, with a taper that reduces it by £1 for every £2 of net estate value above £2 million. In the Mrs X case described earlier, the RNRB was unavailable because Miss B was not a direct descendant, increasing the IHT liability by £70,000. Executors should verify the undisclosed beneficiary’s relationship to the testator before claiming the RNRB on the IHT400.

Q3: What happens if the secret trustee dies before distributing the assets to the undisclosed beneficiary?

If the secret trustee dies before distributing the assets, the trust does not automatically fail. The secret trust is a trust, not a personal gift, so the assets remain held for the undisclosed beneficiary. However, the trustee’s personal representatives (PRs) become responsible for administering the trust. The PRs must identify the undisclosed beneficiary—which may be difficult if the trust was truly secret and no written records exist. If the beneficiary cannot be found, the assets may be paid into court under the Trustee Act 1925. For IHT purposes, the assets are not part of the secret trustee’s estate, so no IHT is due on them from the trustee’s death. However, the PRs must file a separate IHT account for the trust if it continues beyond two years from the original testator’s death.

References

• HMRC, 2024, Inheritance Tax Statistics: 2023-24 Receipts and Forecasts
• Office for Budget Responsibility, 2024, Economic and Fiscal Outlook – March 2024
• Law Commission, 2023, Making a Will: Report on Execution and Revocation
• HMRC, 2022, Trust Registration Service: Guidance for Trustees and Agents
• HM Courts & Tribunals Service, 2023, Probate Practice Direction: Secret Trusts and Undisclosed Beneficiaries