Breaking news! In early Feb 2019 we finally found a solution to install a VMC (extractor fan) in the family bathroom! We have no access to the crawlspace between the first floor ceilings and the roof, so it posed a conundrum. However, hats off to my amazing builders, who climbed up on to my VERY tall roof, took several roof tiles off, broke through the crawlspace ‘skin’ and then the concrete ceiling of the bathroom. They were then able to install the VMC and hook it up to the light switch, so it works when the light is on.
And while I had them, I got them to replace my Victorian style rain-shower, as the hand-shower part was slightly fidgety to get so that you had full force on one or the other of the showers. So we have a brand new shower up there too!