Programming an electronic till to suppress the recording of sales amounts to tax evasion and HMRC can impose some serious penalties on retailers who do this.
HMRC are initially seeking out the producers and promoters of electronic till software that can be used for electronic sales suppression (ESS). Once they find a software distributor that is selling ESS software they will track down all the businesses that have purchased the software.
If HMRC discover that you have purchased ESS enabling tools they will send you a notice to remove the software from your tills within 30 days. If you ignore that notice HMRC can impose a penalty of up to £50,000.
To avoid such high penalties take extra care when purchasing or upgrading your till software. Check the credentials of your software supplier and make sure you are buying an authentic product.