excuse the imprecise terms & long Q - to preface I’m ok with the wiring in this case, just a basic Q about starting; currently in place is a 2 gang switch and a fuse switch alongside (for a boiler) - embedded in the wall is one metal box, with two sections for the gang/fuse. I need to install a timer for a combi boiler. I understand the best process is to replace the 2 gang with the timer (which is designed to directly replace a 1 gang switch) and install a 1 gang taking care of the remaining connection. MY PROBLEM IS - can I remove the current 'metal box' easily and what exactly do I need to buy, that will house the 1 gang switch, fuse and keep the timer in place. I think I need a 'metal box' for a 1 gang switch and virtually the same for the fuse and timer. So do I fit 3 'metal boxes' concurrent in the space? What are the boxes called? Where is the best priced place to buy them?