I have just re-scanned the discussed photo at a highter resolution, as although there are no cap badges, each have collar badges, which can now be seen quite clearly. If Beedan has no objection, I would like to post the photo, as although I can see that Sid is wearing what I believe is service dress, Tom's uniform is of a completely different style, and I have no idea why, but would love to know! Tom enlisted into the ASC on 15 November 1915 and was discharged from RASC on 30 December 1918. Other photos I have of Tom show him in service dress whilst in the ASC band.
Thanks - Jo