It's as I thought, it's not 100% pure Scotch Whisky but what's called and "admix" made from 100% Pure Malt Scotch and a local neutral/whisky type spirit. These admixes sometimes only contain 5 or 10% malt and the very best possibly 25%. Nowhere does it state 100% Pure Scotch Whisky.
It's definitely not a Gilbey's bottling as the label would state either their name or the name of a subsiduary company and to make it certain the bottles branded by Margant.
Sorry to disappoint you but there was a time when there were a lot of this happening, mainly from the 1930's through to the late 1950's. The formation of the Scotch Whisky Association quickly brought this to a stop.