Stephanie Sharpe, of accountancy firm Moore Kingston Smith, said a family could fall foul of the rules by accidentally undervaluing a property.
For example, if the deceased had a £2.5m estate, leaving a £320,000 holiday home to his son and everything else to his widow, the family might assume they did not need to fill in form IHT400 because the estate was below the £3m threshold.
However, if it later turned out the holiday home was worth £330,000 at the date of death, then the form should have been completed and inheritance tax paid. This is because not all assets passed to the widow, so the whole estate cannot be considered exempt, and the value of the £330,000 second home exceeded the £325,000 nil-rate band.
Ms Sharpe said: “The rules defining an excepted estate changed in January 2022 and HMRC is now paying particular attention to low value estates or those claimed to be exempt.”
She added: “These potential errors are more likely in high-value estates so the cut-off for any exemption from filing an IHT400 is £3m.”
