Info on MKIII Reflector Gunsight

Hi,
I am new here... and I was wondering if you guys would be kind enough to give me any more info on this great piece of history that a friend of mine owns.
It is of course an Type 1 MKIII reflector gunsight.
It's according to him fully working.
Do you have any idea which type of plane it would have come off of?
It has the following inscriptions Store Ref No8b/2518
AM Serial No 14185/44. The 5 could be a 6, the stamping is not clear.
Please find photos of it attached.
He also feels that it is of considerable value, but does not really seem to have an in depth knowledge of it.
Thanks in advance for any info you can provide me with.
rgds,
James

Looks like a Pilot's Reflector Gun Sight Mk.II L

This was a modified Mk.II* sight where the pilot could adjust the angle of the reflector (note the 'degrees' nob) and depress or elevate the line of sight. This was used for rocket firing and would most likely be used in Hurricane, Beaufighter and Typhoon aircraft.