They work on a case by case basis

HMRC say that they judge every case on its own merits. That may sound sweet but it’s actually a huge pain: it’s expensive and it’s time consuming.

Let’s say there are two freelance journalists, writing an identical number of articles for identical markets. They have claimed buying newspapers and magazines as expense - and rightly so.

In an investigation it’s the job of the Inspector to reduce those expenses. They may well argue that some personal enjoyment was gained from reading the paper, or that they might buy a paper anyway, even if they weren't journalists or even that the journalists wrote features so the news elements of the paper were not relevant!

One journalist might cave-in and accept an adjustment in his expenses for personal use (victory for the Inspector kerr-ching) while the other may stand up for what what is common sense, insisting that he be allowed to claim the full amount.

So - and this is really common - two people with identical work and expenses can be treated and taxed completely differently.

When HMRC say that they judge every case on its own merits, what they actually mean is that they will get whatever they can from whoever they can whenever they can.