Hi, Says Ariel, front hydraulics suggest post 1945 Regards Vintman I think it's an Ariel 350, model NG or NH, probably built between '46 and '51 (until '45 they used girder forks and in '51 they changed the badge). It's not a 500, those have larger fins on the cilinderhead.
License number A7936. A = Stockholms stad. Motorcycles was unfortunately not in the Bilkalendern books.