Wealthy families may have underpaid almost £400million in inheritance tax last year, according to new figures. HMRC suspects up to £392million in inheritance tax (IHT) was underpaid by wealthy individuals in the year to March 31, 2026, according to TWM Solicitors, a UK-based law firm specialising in areas including private client and family law. The potential shortfall has risen by 14% from £344million a year earlier, though the £392million figure represents the maximum potential tax owed before HMRC completes its investigations, rather than confirmed unpaid tax.

Duncan Mitchell-Innes, Deputy Head of Private Client and Partner at TWM, warned that mistakes can occur when families attempt to deal with the complicated inheritance tax rules themselves.

He told IFA Magazine: “The IHT rules can be complicated and, for executors trying to complete the IHT return without professional help, there is scope for misunderstanding or not being aware of the rules, leading to an inadvertent underpayment of IHT.”

HMRC defines wealthy individuals for these purposes as people who had income of at least £200,000 or assets worth more than £2million in any of the previous three years.

The tax authority can investigate whether valuable possessions such as jewellery, watches and paintings have been left out of probate records, or whether homes and artworks have been undervalued.

Meanwhile, inheritance tax revenues continue to rise. The latest official HMRC data shows the tax brought in £3.2billion between April and July 2026 — £100million more than during the same period last year. June 2026 produced the highest monthly inheritance tax receipts on record.

The standard tax-free allowance currently stands at £325,000 and has remained at that level since 2009. It is now confirmed to remain frozen until April 2031.

A major change is due in April 2027, when most unused pension funds and pension death benefits will be brought into a person’s estate for inheritance tax purposes.