IHTM28060 | Liabilities: investigating liabilities: Capital Gains Tax (CGT)
From HM Revenue & Customs · Inheritance Tax Manual
In general you can accept the value of any deduction for CGT as claimed. This includes most estimated liabilities. But if the estimated liability is substantial you should consider asking the taxpayers to confirm the final figures when known.
You should check to make sure the transaction that gave rise to the CGT liability is reflected in the deceased’s estate (IHTM28061).
Remember, the size of the CGT deduction claimed does not necessarily reflect the value of the assets that have been gifted or sold. This is because the tax is charged on the increase in value over and above inflation and not the value of the asset itself