"Made like a gun, goes like a bullet"
So many Enfield stories. So little time!
You hit the nail on the head old chap . Indeed it is a sidecar windscreen ;http://cybermotorcycle.com/gallery/components/images/Easting_Windscreens_1923c.jpgI used to have something similar that was colloquially referred to as Bunty's weather warrior , very useful for solo use during foul weather- byJove .Can't remember the maker though , might have had it made by my saddler - eh what .Last I saw of it some rustic wretch had purloined it for his tractor - bloody scoundrel .Your servant Bunty, etc.
Bunty found it. Here's a shorter link to Easting windshields. What an amazing gizmo. You could get them for your rumble seat, too.