On most new builds you see the bathroom/en suite fan isolator located outside the bathroom above the door so they are convenient to switch from the point of servicing but not convenient to use as the general on/off switch. Most of these fans are then wired into the lighting circuit so they come on when the lights are turned on. If you do not want that and require a seperate switch then if that is going in the bathroom that will have to be a pull cord type and will not need to be a 3 pole type neither will the isolator unless it is being wired through the light circuit.

Richard