How to do a compliance check: types of compliance checks: joint working with other government agencies: need for privacy during joint visits
If you cannot lawfully disclose to the other agencies present the information you are seeking to obtain you must not question anyone about a person’s tax affairs if another agency is able to overhear the replies.
This is because you should carry out your duties in a professional manner, respecting confidentiality and privacy. You should be discreet when on visits or at meetings. Bear in mind that people will not usually wish to discuss their tax affairs in front of their staff, customers, other persons or their family, see CH201300.