The telescope appears to be a commercial type Aldis Bros. made up after WWI, probably using lenses and parts left over from their WWI production of scopes for SMLE and P14 sniper rifles. They are very similar to, but not the same as the WWI scopes. The distinct downward cant of the scope apparently indicating that the owner intended to use it for longer ranges, which I suppose the cartridge is very capable of.
It is zeroed for windage by removing the cover on the object lens housing and rotating the prism therein with a flat key made to fit the two slots. This also throws the elevation adjustment out, so that has to be reset aftwards.
Here's a sheet on the scope.
Were it not for the beautiful condition of the rifle and the post-war scope, one might think it was set up to "bash-in" German sniper shields, as quite a few Express rifles were used for this purpose in WWI.