DWP pension entry causes tax miscalculation

I have completed my return so am unable to view the exact pages I need to discuss. This is from memory. I entered my P60 income which showed I have already paid circa £2000 tax I wrongly entered my DWP pension in the "Lump sum" box whereas I should have entered it in the "Total annual" box. The figure was calculated as 13 x 4 weekly payments from my bank statement. I also entered £800 in the Gift aid box. My tax due calculation was asking me to pay £200 more than the actual amount I had calculated. When I changed the Gift aid amount to £2000 my tax due calculation was asking me to pay £500 more than the actual amount I had calculated. When I changed the Gift aid amount to £zero my tax due calculation was correct. It took me ages to find where the problem was but when I eventually moved my Pension entry to the correct box and re entered my Giftaid everything worked correctly. The question I have is "Why would I have to pay tax on my Gift aid donations if I have received a lump sum DWP pension payment, regardless of its value?" I entered a figure in the wrong box and I cant be the first person to do that but it does not make any sense to me. Is the system at fault or have I missed a point?

Hi 

You would have been asked to pay tax on the gift aid based on the other details you entered. your income was below the personal allowances and no tax paid.

As you have stated payments under gift aid, the charity only gets relief if you have in fact paid tax.

If this has not been paid by you at source, you are then charged for it in your calculation.

The lump sum State Pension is not counted for this purpose,

Thank you. 

This is NOT the case As I stated at the top of my message , I had entered details from my P60 s showing gross private pension income of circa £22K and tax paid of circa £2k. This is plenty to cover a mere £800 Gift aid. Hence my concern