Matters of material significance
Charity scrutiny is not only for the trustees. Auditors and independent examiners owe a separate statutory duty to the regulator, and it overrides confidentiality to the client.
The reportable matters cover serious concerns including dishonesty or fraud, significant loss of charity funds, and matters suggesting a serious breach of law or the governing document. The duty applies whether or not the trustees are told.
This is worth knowing before you appoint someone: an examiner who spots a serious problem is obliged to report it. See appointing an independent examiner.