Unblemished UGB found in the garden. Pre 1968?

[Leftofcentre]

Hello folks. We are having some work done on our land and i found this bottle just under the surface. It is complete and in perfect condition. It even looks quite modern with a mould seam along the narrow edges all the way to the lip. However the marking on the bottom lead me to believe it is pre 1968.
The images arent very clear but on the base it says W 991 6-OZ L 13 UGB
Can anybody shed any light at what may have been inside it?

 

[Newfie treasure hunter]

Pretty common I believe. Not shure how old but probably anywhere from 1940s-1960s I'd say. Still pretty nice to find in that good of shape in a garden!