A 3-ton CMP (Canadian Military Pattern) lorry from the look of it. I don't know them well enough to say if it's Ford or Chev or an 11 or 12 pattern cab though. Probably a 12 cab in the Middle East ?
The pillion appears to be a canvas covered Dunlopillo as also used on Nortons from contract C10217 built very late 1941 and mostly early 1942. Not having the BSA info at hand I assume this BSA is built around the same time?
Re: BSA M20 in the North African campaign. (Edited by Author)
Steve had uploaded the image using Imgur which now blocks UK IP addresses as it declines to comply with the ludicrous Online Security Act. Basically the internet is now broken in the UK and it's only going to get worse. Still, think of the Children who have been saved ! You're probably all going to have to use VPNs if you want to access in future.