In a formal inquiry into a tax return, an officer is statutorily entitled to ask for information which he requires in order to determine whether the return is incorrect and, if so, to what extent. Information about relatives may be relevant to that inquiry. For example, in a case where the business records are incomplete, the best way to measure the true level of income may be to estimate the taxpayer's expenditure. In that case, information about the cost of maintaining dependent relatives and their contribution to household expenses may be relevant, and may be legitimately required by the investigator.
The results of any inquiry into one family member may show that there is a risk of tax evasion by another. There is no bar on the Inland Revenue using that information in deciding whether to inquire into the tax affairs of the second family member.