Although lacking in detail, even after enhancement, the collar badge looks strongly like that of the 3rd Carabiniers (Prince of Wales’s Dragoon Guards), it’s certainly the only badge I can find in my books or online of a cavalry regiment that has such a large Prince of Wales feathers emblem with two small “rods/spike” like objects above it. With all the other badges that incorporate the feathers, the emblem is much smaller, show the flags of crossed lances above it and other features negate it from being any of those.
That makes the photo of the seated soldier, that I think may have been an army picture, post 1928.
That was after the regiments was renamed the 3rd Carabiniers’ from the 3rd/6th Dragoon Guards that itself was formed in 1922 from the merger of 3rd Dragoon Guards (Prince of Wales’s) and the 6th Dragoon Guards (Carabiniers). If the photo of the mounted soldier is the same man, then that too is the same post 1928 period.
For an image of the collar badges, see http://www.endicimilitaria.com/viewphoto.php?shoph=50133&...
There’s a clear photograph of the uniform in the 1920’s at http://www.3rdcarabiniers.org.uk
> photo albums > ?????? Squadron (scroll down) > Arthur James Thorn 20’s.
I’m sure someone on the forum or at the regiment’s museum will be able to confirm what I say.
The regiment was based in the UK throughout the 1928-1936 period, so it’s unlikely you will be able to confirm anything via British Army Campaign medal rolls and his army record will still be with the MoD. Although in theory next of kin can order documents without his army number, information on other boards/forums suggest it may not be successful. See http://www.veterans-uk.info/