I'm pretty sure that the engine is an Enfield one but the gearbox and primary cover don't look right for an Enfield. Equally sure that Enfield frames to match that engine were all single downtube whereas that one's double. Whatever its origins, it looks like it gets at least a few miles under its wheels.
I had one of these as a winter bike in the mid 1980's (a red one)I kept it for 17 years dispatched on it for a while then sold it running on it's standard untouched engine with 112000 miles on the clock ( I really wish I hadn't) all this time I went through probably another 30 or so bikes so when I saw this cheap I had to have it. Since sold as I failed to recreate the spirit of the crazy 80's/90's , probably a good thing as|I'd either have no license or be dead !
I brought this for my lad a couple of years ago XL125S a dutch import built 1993 but for some reason to 1970's standards (6 volt electrics, drum brakes,twinshock) but it was then registered in the UK as a 2000 model ? But before he was old enough I decided to use it for green lanning around Wales with the Green land crew. Here is a pick of it after a local outing. It really did work well and ran rings around some people on much bigger more modern bikes, it's lack of power low/ height being a distinct advantage, although when the drums filled with muddy sludge the brakes didn't work which was very thrilling down rocky stream beds and steep banks .My lad never got it and ended up with a KMX125 which I also took out.