ESS – electronic sales suppression – is where a business uses a tool to either hide or reduce the value of individual transactions on its electronic sales records, either at, or after, the point of sale.
The ESS tool is a piece of software, computer code script or hardware. HMRC have issued a document on this subject and have introduced a disclosure system for use between 6 January and 28 February 2023 which might lead to reduced penalties for disclosing it, rather than waiting for HMRC to “discover” the use of such tools.
See: https://www.gov.uk/government/publications/compliance-checks-electronic-sales-suppression-ccfs68