Almost a quarter of all estates that pay inheritance tax are investigated by HM Revenue & Customs (HMRC), a freedom of information request by Quilter has found.
In the 2018/19 tax year, there were around 22,000 estates liable to pay inheritance tax (IHT) and, of those, 5,537 - just over 25% - were investigated by the taxman.
As the following table shows, since the 2013/14 tax year, HMRC has investigated more than 5,000 estates every 12 months while, in 2013/14, more than 6,000 investigations were opened.
Quilter tax and financial planning expert Gordon Andrews said: "Inheritance tax is infamous for being not only disliked but complex and at times deeply unfair. On top of everything, there is almost a one in four chance HMRC will investigate your estate.
"Over the past number of years, politicians have been keen to show they are cracking down on tax-dodgers and IHT is one of the departments HMRC has been throwing resources at."
Andrews said people typically were not trying to defraud HMRC but, given the complexity of the system, it was "no wonder things go awry".
He continued: "Under the current rules, for instance, if a pension transfer is made while someone is in ill-health, then there is a risk that HMRC will challenge the IHT-free status of the death benefits if the person passes away within two years of the transfer.
"This is absurd at best and perverse at worst as it is essentially penalising people for appropriate tax planning."
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