I've had a look at the only report I have TD/RIFLE/5 20 Jan 75, which is a comparison trial between the SP 222 Singlepoint and the L2A1 SUIT sight. Unfortunately although there is a ton of tables, graphs and photos of various target ranges there are no images of the Singlepoint Sight and Mount. I think these might be contained in an earlier report that I don't have.
I think depending on the shade of gray paint it might be
Belgium
army issue. The colour would need to be checked against something like a ABL marked SAFN49.
I would tend toward the mount being used with a Singlepoint type lightweight sight. According to the report the mounts for the trial were supplied by Enfield, if you check the mount can you find the Enfield logo on it?
Ohhhhhhhhhhhhhhhh as an after thought it might be for use with the BSA Unisight? Its a tiny sight that would fit the 3/8 in. rail.
https://www.milsurps.com/images/impo...unisight-1.jpg
If you ever want to get rid of the mount I would be interested in it.