Up to £14.3 billion of tax is suspected to have been unpaid by wealthy individuals and their firms at the end of the last tax year, according to data from HMRC.
The data from the UK tax collection authority included £343 million of potentially under-declared inheritance tax (IHT), around £785 million for company research and development claims, and £3.2 billion of potential under-paid tax from international firms.
These amounts are put into a sharper spotlight amidst the growing public debt and efforts by Chancellor Rachel Reeves and the Treasury to gee up tax collection.
IHT 'tax under consideration', the tax collectors term for its estimate of the maximum potential additional tax liability before a full investigation has been carried out, was up from £325 million in the previous year.
The IHT underpayment number highlights growing concern over under-reporting during probate, said law firm TWM Solicitors.
The firm warned that the figure is likely to increase as new IHT rules take effect from April 2026 that include a £1 million cap on business and agricultural property relief, a 50% cut to AIM share tax breaks, and IHT on inherited pensions starting April 2027.
“The penalties that HMRC can impose for tax avoidance and evasion are very substantial so it’s important that IHT calculations are done properly with professional advice,” said Laura Walkley, partner at TWM.
Common triggers for investigations include undervaluing property, failing to declare valuables, or misreporting gift dates.
HMRC has reportedly been using digital tools such as Land Registry data, Google Street View, and property contents insurance to detect discrepancies.
TWM anticipates a rise in IHT disputes between executors and HMRC as the tax burden on estates grows and scrutiny intensifies.
Tax under consideration is not necessarily tax that is owed or unpaid, HMRC stressed, but suspected of being so before any investigation is carried out. "In many cases, when we have looked at the full facts, it becomes clear that there is some lesser liability or even no further liability at all."