Lunchtime, so a spot of research... [FX: Pokes internet with a stick]
...looks like it was originally a Naval item, a post on BOCN got a response that it was probably from a Scott-Vickers gun director, and used for target identification rather than as a gunsight, which would explain the high magnification option.
http://www.bocn.co.uk/vbforum/thread...ower-Telescope
Another link provided a photograph of (presumably) an original, though I suspect The Mad Brass Polisher has had his evil way with it:
https://www.the-saleroom.com/en-gb/a...8-a42400266ffd
An un-polished example:
https://www.the-saleroom.com/en-gb/a...0-a3fd00d6ba09
So, a WW1 naval fire control telescope rebuilt/repurposed in WW2 as an artillery or tank gunsight?
Chris.