Socialist opponents of flat tax will often use the arguments that progressive taxation is a fairer form of redistribution and that flat tax would unfairly compensate the well off.
I thought I would challenge this assertion by looking at some actual figures. The table below lists a selection of salaries from £10,000 to £200,000 along with the actual tax paid for this tax year. The marginal tax rate is simply the percentage of that gross wage that goes straight to El Gordo.

I should point out that these are income tax calculations and do not take into account any means tested tax credits that may be awarded to lower earners. The tax figure includes NI contributions.
The next table illustrates a flat tax system. The rules are simple: the first £18,000 of your salary is tax free. After that the tax rate is 45%. NI would be scrapped. 45% sounds like a lot, but check out the figures and see for yourself:

Obviously, the first thing you notice is that salaries below £50,000 will benefit enormously from this structure. The second thing that jumped out at me was that this system is more progressive than the our current taxation system. Wages from around £85,000+ would attract more tax than they do currently, and the higher you go, the more painful it gets.
I suspect that the above figures would not work in reality as the net tax take to the Treasury would drop dramatically (If somebody could find me a salary distribution scale for the UK I might be able to guesstimate the net effect).
With that in mind, I tweaked the input parameters (all two of them) to see if I could create a little more balance: a £12,000 tax free allowance and a tax rate of 42%.

This time the lower earners are still much better off, the middle income earners are pretty much unaffected and the higher earners still pay more than they do now.
Tax Credits could be scrapped. Thousands of civil servants would no longer be required. Self Assessment tax forms would only have two numbers to fill out. And finally, the lefties would get what they always wanted: a proper progressive tax system that redistributes wealth to the low paid. Automatically. No forms to fill out. No “means tested” shite to put up with. You simply get to keep what you rightfully earned.
Surely that is better than what we have now?