I can buy a multimeter, but what should i check for exactly? Would i not still have to remove (or box) the cable?
The best way would be to (with the power off) Put each core into a separate connector block (so 4 total)
If you don't know which is the switch wire: reconnect your switch, then between one set of red and black, test for continuity - if there's none, operate the switch, if there is, operate the switch, after operating the switch it should be the opposite of what it was originally, if it's not the switch nothing will change + repeat on the other cable.
Now go to the closest rose and disconnect one cable from the loop. You're going to want to put these into a connector block in case you remove the loop in rather than the loop out.
Re energise and (assuming the light you have disconnected from still works) test for live between live and neutral at the cable you wish to disconnect. If you have voltage it was not the correct light, repeat for each rose until you find no voltage at the cable you wish to remove.
You can then connect both the live and neutral together into one connector block and push them into the void. This will show anyone they are no longer in use (as they would blow the fuse if they were energised) and will stop them coming into contact with anything else
You can test the connector block safely via the screw terminal, so make sure you don't have any wires sticking out the other end, this should stop you getting a nasty shock.
I'm sure someone else can add some tips too
