NOVELTY - A panel (2) comprises main body portion having 2 opposite end portions (6) each having a transverse anchoring slot extending from their lateral edge. A length of each transverse anchoring slot (8) is half a width of the panel. The panel is anchorable to a second like panel by mutual interlocking of the anchoring slot in an end portion of the panel with a corresponding anchoring slot in a corresponding respective end portion of the second like panel when in an inverted orientation with respect to the first panel.    USE - Panel for forming side wall of box structure, which is a compost box (or bin) or a planter (claimed).    ADVANTAGE - The panel is capable of providing a simpler modular system, for quick and easy self-assembly by end-user, involving few structural elements and in particular a specially designed shape of wall panel for building up the box structure sides walls.    DETAILED DESCRIPTION - Panel (2) for forming side wall of box structure comprises main body portion having 2 opposite end portions (6) each having a transverse anchoring slot (8) extending from their lateral edge. The length of each transverse anchoring slot is half the width of the panel. The panel is anchorable to a second like panel by mutual interlocking of the anchoring slot in an end portion of the panel with a corresponding anchoring slot in a corresponding respective end portion of the second like panel when in an inverted orientation with respect to the first panel. The lateral edge of the main body portion of the panel further comprises engagement formations for assisting seating and anchoring of the panel to another like panel above or below it when in place in the side wall of a box structure. An INDEPENDENT CLAIM is included for a method of assembling a box structure comprising (i) providing identical panels; (ii) assembling first set of the panels into a first level of the structure by orientating the panels as their respective end portions are mutually interlocked via their respective anchoring slots; (iii) assembling second set of the panels into second level of the structure on top of the first level, with the engagement formations in/on the upper lateral edge of the panels of the first level being engaged with the corresponding engagement formations in/on the lower lateral edge of the panels of the second level; and (iv) optionally, sequentially assembling third and any subsequent sets of the panels into third and any subsequent levels of the structure on top of the previous level by corresponding further respective steps corresponding to steps (ii) and (iii). Each end portion terminates beyond the respective anchoring slot in a tongue portion (6a). The engagement formations take the form of corresponding elongated tongue (10) and groove formations. Both lateral edges of the panel are formed with a groove feature, and a separate, loose, tongue strip element is provided for insertion into the groove on an edge. The loose tongue element is securable in place in the assembled box structure including the panel by an adhesive.    DESCRIPTION OF DRAWING(S) - The drawings show a side face view of a wall panel and a front perspective view of a compost box.    Panel (2)    Opposite end portions (6)    Tongue portion (6a)    Anchoring slot (8)    Tongue (10)