Gift Aid is reclaimed by the charity from the tax you pay in the tax year the donation was made in. Your home address is needed to identify you as a current UK taxpayer.
I want Arthritis UK to claim Gift Aid on my donation made today, and any donations I make in the future or have made in the past 4 years. I am a UK taxpayer and I understand that if I pay less Income Tax and/or Capital Gains Tax than the amount of Gift Aid claimed on all my donations in that tax year it is my responsibility to pay any difference.