I screwed a small eye bolt into the skirting board, run the chain through the eye and through the padlock on he box.

It seems that the objective is to stop a visitor, (workmen etc), from picking up the box and taking it away.

Different areas have different rules. Some say put it in the loft. Some tell you to chain it up, and some tell you not to chain it up so if there is a fire you can pick up the box and chuck it out of the window. (To stop the firemen being blown up).