Tax due on Gift Aid payments

I've just completed my self assessment but not submitted it. When I reviewed it I saw the line "Tax due on Gift Aid payments £1564 x20% £312. i.e., The return suggests I am liable for £312 in tax because I donated to charity. I am an additional rate payer and I see no reason for this line. Can someone give me a hint to why it is there?

Hi 

You would only be due to pay tax on this if you hadn't paid enough tax to cover it.
The relief is given by extending the basic rate band which should show on the calculation.
If you submit the return and contact the Self Assessment department after 72 hours we can view the calculation. You can find our contact details here:
Self Assessment: general enquiries

Thank you