Not a G80 - its a trials model either G3C matchless or 16 (350) 02 18(500)c Ajs. Pretty sorted rigid trials machines. apart from the chopped rear mudguard that looks pretty standard. Heavy but really sweet handling (in the sections that is) and not bad ground clearance for a rigid.
The springer shown in the pictures is also a nice un' the pukka trials frames are extrememly rare.