I've fitted the fan, a 240v pull cord operated one, from Blauberg. I almost didn't fit an extractor fan at all today because I thought that the space between the underside of the roof and a horizontal beam just behind the eaves was too narrow to get my insulated ducting through, but as it was the final foot or so, I just cut the insulation off that part of the ducting and pulled it through from outside, and had no problems. I connected the extractor fan to the bathroom ceiling light cables, it's mounted about a foot away from the light, so it was easy to do. I didn't bother with an isolation switch. I figure that I am going to live in this house until I die, and therefore it's no problem for me to turn off the lighting circuit if/when I ever want to change the fan. (Actually I turn off everything at the consumer unit via the main switch whenever I do anything involving electrics in the house. I don't trust whoever wired the house and it's never been a problem. I only turned off the electricity for about five minutes to wire in the fan today, so no problem.) I used a 100mm pipe and pipe adaptor (see one of my other posts about this) to slip over the top of the fan, otherwise it's impossible to get the ducting on, it's much easier this way anyway, because you can slide the ducting over just the pipe adaptor, which you can hold any way you like (unlike the fan, which is obviously mounted in the ceiling below at this point) and then put a cable tie around it, slide it into the 100mm pipe, and then slide the 100mm pipe over the top of the fan, and that's it, finished.
Adding an isolation switch would have been a lot of extra work and it's totally unnecessary in my opinion. I would always use a headlight when trying to fit electric cables into a fan anyway, I wear glasses and the extra light helps me.
