Group 1
Typical individuals, SMEs, etc.
and
Group 2
Large corporations, politically and otherwise connected individuals
Group 1 come under enormous scrutiny and given the powers that the revenue has this can be a ruinous process, which we all fear. (Thus, there's a large business in selling "audit insurance" to SME's to cover the business disaster that is a Revenue audit.)
Group 2 get very little real scrutiny. It's partially just that the richer you are, the more you can afford fancy tax lawyers to find loopholes in the first place and partly a matter of political will. But a big issue is simply that compared to a large transnational, the Revenue is up against it. Some big corporation (e.g. Vauxhall/GM at one point) employed more tax experts and lawyers than the Inland Revenue had in the whole region where the headquarters were.
I think I remember that the 400 tax collectors in charge of large companies in France collect as much money for the State than the other 160,000 employees of the Ministry's other tax divisions. In the long run, we're all dead. John Maynard Keynes
It can get sleazier since with enough tax paying clout and and a decent payroll (ie jobs thank can be relocated) a company can still cut a deal after being caught paying insufficient taxes. Once the auditor has told you how much back taxes you owe, the haggling can begin in earnest and there's now way in hell the big players ante up the full amount penalty and all.
