Petition close tax avoidance loophole for self employed

Why doesn't the Government raise tax revenues by closing the tax loophole that allows the self employed to pay themselves a very low wage (paying either none or very low level of income tax) and then to pay themselves large dividends each year that are only taxed at 10%. This is unfair to those of us in full time employment that pay high rates/levels of tax, and is used by the self employed simply to reduce their tax bill significantly and increase their disposable incomes.

Given the increasing numbers of self employed these days (e.g. plumbers/builders/contractors etc), I would imagine that Government could raise significant additional revenues to reduce the national debt and be seen to be introducing fairer tax regimes, by ensuring that these people also pay their fair share of tax as do the rest of us !