Very nice find, Loach369.
A friend of mine had a similar find in a Scottish gun shop a few years ago, but the best thing about it was that there was a .177 barrel in the box with the original .25, and the box was packed full with period pellets, including three boxes of Webley .25, one of which was part used, two sealed tins of Webley .177, 10 boxes of Caledonian .177 x 100, plus a couple of part used tins of Webley .177.
He sold me all the pellets on his return, but it took me several years to get the rest.