Hallo Cottack. As Quizmonkey says, this is called Gift Aid. The way it works is that, if you want to make a donation to a charity, and the charity has a registered number, the charity is able to claim back the amount of tax that you paid on the amount that you've donated. So it's the charity that gets the money, not you. First of all you have to be a tax payer, and secondly you have to indicate that you want the donation treated for Gift Aid. Hence the little square that you mention. This applies for all registered charities.