I am advised by the Revenue Commissioners that where a person, who does not wish their identity to be disclosed, passes information to them, it is their policy to protect the identity of that person.
However there may be circumstances where disclosure would be ordered by a judge, for example, if the information triggers a criminal investigation and a prosecution, it may be a matter for the Trial Judge to determine whether the interests of a fair trial require disclosure of the name of an informant.
There is also strong protection under the FOI Acts for the non-release of the identity of a person who passes information to Revenue. However for completeness, it should be also noted that every FOI case is subject to review on appeal by the Office of the Information Commissioner and that in such circumstances a situation might possibly arise where Revenue might be obliged to disclose the identity of such a person.
It should also be noted that individuals always have the option to pass information to Revenue anonymously.