if you intend to not replace the fan but just fit a spotlight ,the line ,neutral and earth conductors that are connected currently will be needed to connect up to the new spotlight. to safely isolate the circuit you should do this at the consumer unit or fuseboard. Do NOT try to do it at the switch. all the conductors that are connected to your switch ( red and black) are all LIVE conductors. I think the switch that turns on your landing light is a two way switch ,and you have one downstairs that can also turn landing light on/off. The cable you disconnected at the switch may well be live, have you put it back ??? the photo does not show all the connections/terminals on the back of the switch very clearly. if you intend to take out the fan/spotlight and not,replace at all then you will need to amend the wiring between the two spot lights ,do you have access above the ceiling ( possibly in the loft ) regards terry.