Hello,
As always, we will need a bit more information and ideally some pictures to establish the exact variant of the Junior you have and to get an idea of it's cosmetic condition etc.
Boxed examples always attract an additional premium especially if in good condition and accompanied by accessories. As a rough guide, Webley air pistols made before 1958 included the B4 post code in the Webley address stamped on the side of the pistol frame. The final iteration of the Junior (Mk2) appeared in the mid-seventies and was manufactured from alloy rather than steel.
Regards
Brian