Penalties for Inaccuracies: Types of inaccuracy: Level of proof
You must check the date from which these rules apply for the tax or duty you are dealing with. See CH81011 for full details.
You must always clearly establish why a penalty is due from the facts.
The standard of proof is the balance of probabilities. This means that on the evidence, it is more probable than not that the inaccuracy was made carelessly or deliberately.
Whilst this is the case whether the inaccuracy is careless or deliberate, the quality of evidence should be higher for the more serious behaviour.