Interesting question. When accountants produce their audit report stating that the accounts show a true and fair view, there's a concept of materiality. That means they can't 100% guarantee that every penny is accounted for correctly but that, in their view, there are no material misstatements. If the company bought a capital item for £100, and didn't depreciate it over 5 years, that's not material. If they find something that would have materially affected revenue or net profit, say by 10 or 20%, then they'd have to highlight it.
If an executive was charged with fraud, and by the end of his trial his lawyers were able to prove all but one of the alleged fraudulent transactions was legitimately incurred, but that he'd claimed a £20 taxi fare when he'd walked, or got a lift, technically he's guilty of fraud but I doubt there would be any punishment.
My former boss on the other hand, was found guilty of concealing tens and maybe hundreds of millions of pounds of insurance claims, which probably impacted the company's net profits by £200m. That's material, and he got 7 years in prison for that.