Its a WW2 Military WM20 bike to the Civilian De-luxe standard. They didn't make the de-luxe after 1940 so this is an early one. It also has a desert Volkes tank top air filter fitted.
I have one of these De-luxe versions but its not complete as yet. Most of the parts that make it a De-luxe are quite difficult to find.
Do you have one?