[lmm]

If you're a "normal" UK taxpayer, you shouldn't have to remember anything for any tax return - just tick the box and give them your name and address (so that they can verify you are in fact a UK taxpayer).

If you're not paying UK income tax, you're not supposed to be able to gift aid it, that's kind of the point.

I can imagine it might be awkward if you're self-employed in the UK or something like that; they don't bother streamlining that case.