Voltage live to neutral low

I’m in the uk on 240V. I’ve got an extractor fan that isn’t working. What I find is that at the fan and the switch that operates it, live to neutral is 160V. Ground to live reads 240 and ground to neutral reads just a couple. This is with the fan disconnected. The rest of the house is fine – it’s just the fan. I presume that it runs off the light circuit which reads as expected.

Anyone any ideas what might be wrong?