I am sure all the Electricians here know this already but the sole purpose of using Red (old wiring) and Brown (New harmonised colours) is to identify the fact that they are all Live conductors. That is to say in spite of the different colours they are all on the "live" side of the circuit in a household lightswitch. If you are not sure about disconnecting any of these wires to put sleeving on, just use the correct colour insulation tape. A small piece to identify clearly its denomination will suffice.
