The tax avoidance “debate” – if, indeed, what we are seeing can really be called a debate – has given birth to the concept of individuals (almost always “rich”) and corporates (usually “multi nationals”) paying their “fair share” of tax.

I don’t think anyone would really object to everyone paying their “fair share”. The problem as I see it, is what on earth does “fair share” actually mean?

I doubt that there are very many people who would (honestly) say that they feel they are paying less than a “fair share”. Let’s be honest, most people would take the opportunity, if offered, to legally lower the tax bill on their income.

So I am left with the feeling that when people talk about wanting everyone to pay their fair share, what they really mean is that ‘other people’ must pay more.

Anyway, cynicism aside, the real problem with the concept of paying a “fair share” is that it can’t be defined in a way that would allow it to be a basis for taxation in the real world. The simple reality is that we all – individuals and corporates – need to have as much certainty as possible about our tax liability. As individuals, we need to know how much of our income (whatever that income may be – e.g. pension, salary, business profits) will be left for us to spend. Similarly, corporates need to know how much of their income will be available for investment in growth or distribution to the owners and that means they need to know what tax they will be paying on their profits. On the other side, of course, the Government needs to know how much tax income it will be collecting. [I know, that leads nicely into a discussion of the tax gap, but not now].

Unfortunately, we can’t have legislation that says “you must pay a fair share” without actually defining a “fair share”. Then you end up with tax legislation that sets out how taxable income/profit is to be determined in different scenarios in order to reach that “fair share”. Which is essentially what we have now.

OK, there is a very strong argument that the current legislation is too complex and doesn’t always achieve its objective. The remedy for that, however, is not to shout about “fair shares” but to work to simplify the legislation and ensure it does work. Of course, it would help if new legislation were introduced in a more effective manner and properly scrutinised by MPs before being enacted, but that debate is also for another time.

The real problem I have with the term “fair share” is that it is used in the current debate as little more than a populist slogan without any real understanding of what it means in practice.

And that, frankly, does nothing whatsoever to move forward the debate on tax avoidance.