Superman 1 dirt bike?????

Ok fellow vitards, me the Mrs and the boy are watching superman 1 while we have dinner this evening and I'm sat waiting for the old dirt bike on the trailer scene..... My favourite part obviously but what is the dirt scooter in question????
It's not a husky or a Harley MX, it's not a Greeves or an Ossa or an early Yamaha MX model, it's def not an early CR or an ajs stormer, don't think it's a dot, a Sprite or a Hodaka.... It's right hand chain, alloy mudguards, what looks to be a glass fibre tank and round side panel mounted low.... Here's a photo I took while I paused the TV.... Any ideas????