It's a letter on one side ... empty ... presumably you need to make the claim within it, and some boxes on the back to fill in details of how you want it paid.
As ever it's in a bloody PDF. And I've not found any software than can create something useful from a PDF (mind you, I've never looked!).
So, it looks as though it just boils down to the letter on the front, which would be something like
"Dear Sirs,
I, commonly called X: of the Y family, as a sovereign Human Being, and thus fundamentally untaxable, meanwhile being Agent and Prime Creditor on Live Birth Trust Account "X Y", reference as per the National insurance Number above, wish to reclaim Income Tax deducted to the Amount £xxx, for the Period yyyy-yyyy.
Thank you.
Yours sincerely with ill-will, frivolity or vexation,
X: of the Y family"
What's the tax on a Human Being? An arm? A leg? Any ideas where that saying might have come from?