On many occassions a useful way of testing the sense of something is to try and phrase the obverse. F'rinstance, 'common sense' could become 'common nonsense' or 'uncommon sense' or if you really wanted to be pedantic - 'uncommon nonsense' - but that sort of cancels itself out.
How about 'working tax credit'? This would become 'working tax debit'.
This is very enlightening. It exposes income tax for what it is. A tax on work, not on income. Income tax is therefore a tax on your time. Or a payroll tax for employers; a cost of employing you.
Of all the taxes that we are forced to pay, I consider income tax - which I shall now call 'working tax debit' - the most despicable, especially so since no State or local government employee pays any income tax at all. The notional deduction for PAYE shown on their payslips is, in reality, just a rebate to the rest of us.