Back in the 90s, I was lucky enough to be an unpaid director in the family firm.
Because of the BCCI scandal along with other egregious examples of huge companies behaving badly, the obvious solution was to crack down on small businesses. So for 3 years all accounts submitted had to be accompanied with a full audit. At the same time, all company directors were required to submit self assessment tax returns.
I did mine with my PAYE income and my directors income of £0.00
Imagine my surprise to receive a demand for £11.
Many hours later it transpired that the PAYE tax tables had a (deliberate) rounding down. Which was fine, but which meant that if you went over someones income with a calculator (which they did) you would have a slight discrepancy of around £10-£20. And because the law was the law, calculated tax due was calculated tax due.
The agent I spoke to was genuinely shocked when I described this as a "nice little earner" and suggested it had the hallmarks of a "scam". I know this because I was told they would report me (remember the past is another country). I then compounded the situation be demanding they report me, only to be told I was getting myself in to a lot of trouble.
It's a serious point. If PAYE tables are rounded down, then slapping the whole country with a self assessment could raise millions.