There is an old tale, A Y service unit took over a liberated manision in Northern France, so recently liberated a lot of Axis equipment was still about. While hunting for souveniers a locked box was found. On opening it, with due force, it was found to be full of Five pounds notes. An officer on the spot pronounced it to be the forgieries they had been warned about. There followed a great spree, lighting ciggarettes , using the notes in the ablutions and other such activities. One soldier decided to keep a couple of souveniers.
Years later after seeing aTV proggramme on forgeries he took them out of intrest to a local coin dealear.
Yep, you guesed! The were real.