Can anyone out there identify a commercial BSA aperture sight for the SMLE. Fits under the locking bolt/safety catch spring.
Is marked with the following patents
26943/07
29844/10
30337/10 followed by the registered design number 575536

The range scale is read from the side and the sight rolls forward and an aperture arm is permitted to fold out when the......., phew, what a complicated set-up! The range and deflectionadjustments are graduated to 10 clicks per revolution. Beautifully made but might be described as '.... not exactly squaddy proof' or in Australiaicon, we'd say '....not something for a Nasho (As we called the National Servicemen....with apologies to them!)

Any ideas chaps? Value? Rarity? Identifying type?