Serious incident
Serious incident reporting is a duty on trustees, and the reporting is expected to be prompt rather than at the year end.
The categories include fraud and theft, significant financial loss, safeguarding incidents, and links to terrorism or extremism. Scotland runs a different regime — notifiable events — with its own list and process.
Reporting is not an admission of failure; failing to report is the more serious problem. See serious incident reporting, and note that a statutory inquiry is often triggered by poor engagement rather than by the incident itself.