There are rules we resent not because they are foolish, but because they remind us of something uncomfortable: that even the noblest human intentions decay with time. Among these necessary disciplines, the auditor rotation rules stand rather solemnly, insisting against our instinct for comfort, that familiarity is the enemy of scrutiny.

The International Standards on Auditing (ISA), particularly ISA 220, offer a gentle warning rather than a prescription. They tell us that independence must be both real and perceived, and they quietly whisper of the dangers of staying too long. More formally, the ethical codes, like those taught in ACCA and ICAEW syllabuses, press the point: for Public Interest Entities (PIEs), the maximum tenure for an auditor is ten years, unless a competitive tender or joint audit is carried out to extend that relationship.

In the case of EY and Stirling Water Seafield Finance, the breach was not dramatic. EY overstayed their welcome. After auditing beyond the permitted decade without a re-tender, they found themselves fined £325,000 by the UK’s Financial Reporting Council.

No embezzlement. No spectacular collapse. Just the quiet danger regulators fear most. Stirling Water, although not listed on a stock exchange, operated major infrastructure, a sewage treatment facility vital to public life, and was thus classified as a Public Interest Entity under UK and EU law.

A PIE not by share price, but by social function. It’s a small, important point. For exams, please always remember: public impact, not public listing, defines a PIE.

ACCA and ICAEW examiners like to test this very point, because it mirrors real life: not all PIEs wear the obvious uniform of public listings. A student who remembers that public significance, not corporate vanity, defines a PIE, is a student who understands the spirit behind the rule.

Regulators like the FRC are not, despite appearances, bureaucratic killjoys. They understand that the real danger does not lie only in corruption, but in comfort. The slow erosion of scepticism when year after year, the same smiles and reassurances pass between people. Hence, the rule: move on after ten years. Resist the lull of the familiar.

If EY’s breach was a failure to keep pace with modern ideals, there is a certain wistful grandeur in the story of PwC and Barclays, a partnership that stretched, astonishingly, from 1896 to 2017. Through world wars, financial collapses, the invention of the internet and beyond, PwC was there, inspecting the books. Such continuity once felt like a badge of honour.

But the world changed. After financial scandals, Enron, WorldCom, Lehman Brothers, trust could no longer rest on relationships.

It had to be verified, renewed and challenged.

Regulators recognised that even a firm as eminent as PwC could not audit a client for 120 years without becoming too deeply enmeshed. And so Barclays held a public tender, and PwC made way for KPMG, not amid scandal, but because even the best relationships must sometimes be brought to a dignified end.

In both cases, the lesson is quiet but profound. Rotation rules are not designed for a world of villains, but for a world of humans, flawed, forgetful and affectionate. In forcing us to move on, even from what seems safe and known, these rules protect a fragile thing: our ability to doubt, to challenge, and to see with clear eyes.