In general, the terms of any arrangement/agreement made in a
telephone conversation with a taxpayer or agent to pay tax or
interest should be confirmed in writing to all the parties
The taxpayer or their agent should also be informed of any protective action that has been taken to secure the IHT charge.
In particular, you should make it clear, if appropriate, that if the taxpayer breaches an agreement, you will issue a Notice of Determination ( IHTM38281). This will avert the need for any delay in the issuing of a Notice.