IHTM28190 | Liabilities: investigating liabilities: local authority payments
From HM Revenue & Customs · Inheritance Tax Manual
Any deductions claimed for unpaid rates or council tax is likely to be small and you can usually accept the taxpayer’s figures. If a larger deduction is claimed you may to check that the sum claimed
does not include instalments due for payment after the date of death, and
has in fact been paid out of the estate.
If required you can find further information about the basis of charge under