1 or more rolls of leftover wallpaper, but NOT ready pasted. (Neath Hill MK14)

I plan to use the back of the paper to make long banners for a party, so the design doesn’t matter. However I’m not sure whether I can paint onto ready-pasted paper, so ordinary stuff is best.
I’m in NE Milton Keynes so closer is best, but I will gratefully reply to any offers.