Political Parties and Elections Bill

Is the choice of language, "without reasonable excuse", based upon a settled body of case law in other statutes where the words have been used, or are we out in open seas? By using it in different contexts, you are going to get different interpretations. For example, on the issue of failure to deliver a proper statement of accounts, it could be a fairly good answer to say, "They were scrutinised by a firm of chartered accountants of high standing and it made a mistake. We only submitted them". The excuse for not making a full report by a particular date may be of a different order from where you are relying on the expert evidence of someone like an accountant. How solid is this as statutory language?