This is actually something I wondered about, specifically, the Gift Aid side of it. The tax you pay is supposed to cover the money the government pays to the charity as Gift Aid. So what if you end up losing your income part way through the year, after the donation has been made, and at the end of the tax year, you didn't earn enough to pay tax. Then surely there is a tax liability for the donation that was gift aided, i.e. you have to reimburse the government.
