It is a receipt. The note size receipts are less common than check size receipts (or checks and drafts) but not rare. There are also letter size receipts. This is an unusual example because the imprint is vertical rather than horizontal.
Seems a pre-printed embossed tax stamp for a recorded corporate transaction. Great Britain used to have such stamps, used by a local tax office to allow advance payment of various regular taxes by private companies. Please check page 11 of this article: http://www.revenuesociety.org.uk/25years.pdf