If you are a firm of accountants
Clients who are relevant organisations for the purposes of the criminal finances act, for example companies, LLPs, partnerships or other organisations, must ensure they have appropriate procedures to prevent the criminal facilitation of tax evasion. You may wish to advise them of the merit of self-reporting any such facilitation of which they become aware and with their authority you could assist in the reporting itself. The self-reporting regime does not allow someone without the authority of the company to report the facilitation to HMRC, so you should only help if asked to do so by the client.
Note that this self-report to HMRC is not the same as a SAR (Suspicious Activity Report) which is made to the NCA (National Crime Agency). If you become aware of or are suspicious that there has been tax evasion at a client, then even if they decide to self-report you will still need to make a SAR to your MLRO, who will then report to the NCA if appropriate.
The guidance provided by HMRC suggests that an organisation may wish to take legal advice before reporting, as well as fully read all the guidance. The self-report is then made through the government gateway and should only include information of which you are already aware. The guidance emphasises that you shouldn’t seek to gather more information, as this could put you at risk. You can find the guidance here.