Limitation of liability by lapse of time: provisional calculations
The issuing of formal assessments is not necessary to bring inheritance Tax into charge. But we do issue informal calculations to advise taxpayers of their estimated tax liability and enable them to make payments in settlement. The calculations remain on a provisional basis until a Notice of Determination (NOD) (IHTM37001) or a clearance certificate (IHTM40010) is issued.
The date on which a payment can be regarded as accepted in full satisfaction will be the earliest date on which a clearance certificate would, if applied for, have been issued. If, in any case the taxpayers or their agents dispute that use of the word ‘Provisional’ prevents time from beginning to run, reference may be made to the Irish case of In re Stopford’s Estate  IR 450. This case held that an account on which the words ‘provisional assessment’ were stamped or written was not ‘settled’ within the meaning of S14 Customs and Inland Revenue Act 1889.
If, at the time of receipt of a payment, there were grounds for regarding the amount of tax assessed as potentially inadequate, and the limitation provisions might apply, you must refer the case to your manager.