I thought it was child benefit that was paid to the mothers to avoid the less father spending it on beer and pork scratchings?
But on the subject of flat tax, I thought the defining feature of flat tax was that the rate was the same for all (i.e. a flat rate regardless). in it's simplest form it's a flat rate on all earnings, no allowance and no deductions, which makes it very simple to collect, particularly from big companies as it is a simple % of their payroll, no need to calculate for each individual.
However it would be very regressive and the lack of deductions is a killer for self employed trades men like carpenters, mechanics etc.
If a carpenter is paid £1000 to make and fit a fitted wardrobe he would be charged £200 with no deductions, but if he paid £400 for the materials, £50 fuel driving about, £25 for wear and tear on tools and consumables and £25 for overheads (failed quotes, office paper, accountant fees, membership to trade body fees etc) he actually only made £500 on the job so ought to pay £100 tax.
What you would find is that people would get around this by the carpenter charging for his time only (£500) and getting the client to buy the materials and tools directly. But isn't that a tax dodge?.....After all the treasury is now out by £100.
Any tax system needs a method for deductions, and deductions lead to loopholes.
Maybe the best way to avoid excessive loop hole use is to publish everyone's tax summary. If I see that a radio DJ is claiming to be a used car dealer or a film producer it becomes obvious they are "stretching" the tax loopholes.
Having no deductions would have the effect of making each transfer of money between parties taxable. If I gave £1000 to a friend, and he gave it straight back to me, he would be taxed on £1000 income and I would be taxed on £1000 income, making £400 for HMRC . So people would structure payment systems to minimise the "payment" of stuff.
Those anomalies exist because of the way sole traders tend to be taxed.
The carpenter is running a business and should be treated as such. Paying VAT on his profits and taking an income from his business.
The issue of self employed taxes is a long list of incompetence by the IR. The 714 system failed spectacularly because the vouchers were made a receipt instead of a bill. Such a simple adjustment yet was beyond the ability of the IR for over 20 years.
The following system, (whose title slips my mind for now), also failed because it was simply too expensive and cumber sum to administer.
Abolish NI. Apply a tax on personal income, without deductions. Apply VAT on businesses.
It really doesn't get much simpler.