Innocent error: did not know that asset or gift had to be declared
In general an error arising from ignorance of the law should not be regarded as innocent. The same is true for an error arising from a failure to read the account and accompanying notes.
For example, when National Savings Certificates (NSCs) (IHTM10091) are omitted from an account taxpayers sometimes seek to excuse this by claiming that they thought these were exempt from inheritance tax (interest on NSCs is exempt from income tax). But the account and notes specifically say that NSCs should be included.