Reg 537.2.1.1 requires each of the live supply conductors to be isolated, except in TN-S or TN-C-S, although manufacturers instructions should be taken into consideration. Most bathroom fan installs, use TP fan isolating switch, so you isolate the fan for maintenance, without having to disconnect the supply to the light (if you have no window, or you like cleaning in the dark), and some customers like to turn them off at night for some reason!
If the fan is a new addition in your bathroom (not a replacement), it would now need RCD protection. If the fan is installed in Zone 1, it would need to be IPX4 or IPX5 if it could splashed by water jets (e.g. shower head). As regards low voltage or extra low voltage, as long as you comply with IP rating, that's your decision.
PS If it is a new fan installed in Zone 1, it should be (cough), notified to LBC.
PPS Humidistat fans, don't get good press on this forum.