Requirements of Regulation 528.1
Unless the segregation requirements of Regulation 528.1 are satisfied, circuits of voltage Band I and voltage B and II should not be contained in the same wiring system as a circuit exceeding low voltage, and a Band I circuit should not be contained in the same wiring system as a Band II circuit.
To minimise the risk of interference between cables of differing voltage levels, every cable or conductor should be insulated for the highest voltage present. Where a multicore cable contains Band I and Band II circuits, as shown in Fig 1, all conductors should be insulated for the highest voltage carried by the cable. One example of this requirement might be where certain cores of a multicore armoured cable to BS 5467 supply SELV equipment, such as a cooling unit having an external condenser requiring a low voltage supply (Band II) and a control circuit (Band I).
Not wanting to derail the Dodgy work pictures thread but a comment was made that a fire alarm FP200 shouldn't be in trunking with 230V band 2 cables.
Above is a quote from an NICEIC article discussing this subject.
I've read that as the cable is "banded" not its voltage going through it.
So if FP200 is being used for a fire alarm it's fine in the same compartment as 230V band 2 cables as FP200 is a band 2 cable even though it only has 24v going through it.
The example of multi voltages in a multicore cable suggests its the insulation level of the cable that is important not the voltage going through it.