From the shambles of the Oscars ceremony to the more serious matters of US lawsuits and UK regulatory investigations, it has been a difficult year for PwC. Its rival KPMG is hardly faring better. The Big Four accountancy firm was castigated by Senator Elizabeth Warren for failing to spot dubious practice at the lender Wells Fargo. Now its auditing of Rolls-Royce is under investigation in the UK after the engineering company admitted bribery and corruption offences going back 20 years.

These scandals are not on the grand scale of the Enron fraud, which led to Arthur Andersen’s demise. Yet they highlight the failure of the accountancy profession and its regulators to resolve, in the intervening 15 years, the fundamental question of how far auditors should be expected to go in their efforts to uncover bad behaviour.

The rules require them to “obtain reasonable assurance” that accounts are “free of material misstatement”. This leaves considerable scope for interpretation. Auditors should be on the lookout for fraud, as well as innocent error, and are expected to conduct checks to try to detect it, especially in areas that account for a significant proportion of a company’s balance sheet.