The cost of 100 000 letters is not insignificant.
Last figures I saw was 10,121 pledges so presumably that means 10,121 letters.
Still a point well made. Postage is a smidgeon under £2,500 at second class.
I could set up standing order online and email the gift-aid declaration if HMRC would accept that.
I will ask the question and post when I get the reply.