Pinched this from another site,says its a BSA M20,looks like a Triumph 3SW/5SW or could even have been a 3HW,has webb girder forks,which were also fitted to some of the SV models.
Below,this photo has been printed reversed,has cropped tank as fitted to 3HWs.
Below,the original info.
I agree Steve, although I didn't know that the Webb forks were ever fitted to SV's. The 3TW had Webb forks with the addition of side check springs. Ron