How to do a compliance check: information powers: third party notice: what is a third party notice
A third party notice is a written notice to a person requiring them to provide information or produce documents reasonably required to check the tax position of another person whose identity you know.
Before you consider giving a third party notice you should discuss your course of action with your line manager.
You may need tribunal approval before you can give a third party notice and if tribunal approval is required you will need the agreement of an authorised officer, see CH225450.
A template IT01_02 in SEES Forms and Letters is available for you to make your report to an authorised officer. The authorised officer uses the same template to reply.