HMRC is relying on information contained in a suspicious activity report (SAR) passed to it by SOCA and its predecessor agency, NCIS, to support an allegation that a taxpayer has substantial undisclosed income. However, the source of the allegation is not disclosed and if the accuracy of the information is to be challenged, a taxpayer needs to apply to the Tax Tribunal for disclosure of the original SAR. This development has implications for the tax practitioners when submitting their own SARs. Since confidentiality cannot be guaranteed, practitioners should write the SAR in a way which facilitates its redaction.