I think I've got to the stage that I'm no longer able to think straight enough to say what is 'reasonable', but I certainly can't get too excited by any of the voltages you've measured. ... but nor does that necessarily mean that there is 'no problem'. However, as I've observed, even these very small voltage differences (whatever is causing them to be present) might be large enough to be felt by at least some people with 'broken skin'.
My wife is very fed up with my scratching my head 
Yes, that's all possible. If the person who comes tomorrow doesn't find anything very exciting, don't forget to show them some of your videos - which might at least get them thinking, and confirm that you have a genuine reason to be concerned (even if it proves to be 'harmless'). It is going to be very frustrating, for all of us, if you end up with no 'proper answer', beyond a suspicion that your own personal sensitivities may underlie what you have experienced!
If we are talking about 'induced voltage', then any changes in any electrical circuits in the vicinity of the bathroom could have an effect. Are there any other electrical things in the vicinity (heated towel rails, fans, immersion heaters etc.) which you could turn on and off to see if they have any effect on the phenomena?
If we are talking about 'induced voltage', then any changes in any electrical circuits in the vicinity of the bathroom could have an effect. Are there any other electrical things in the vicinity (heated towel rails, fans, immersion heaters etc.) which you could turn on and off to see if they have any effect on the phenomena?
Not at all. Some of these 'tingles' threads can be pretty silly, but this one is intriguing, and intellectually stimulating - mainly because of all the 'tests' you have been able to do.
Yes, any of that would might be interesting. However, I don't think that we have yet really established whether there are any 'real' voltage differences between things (as opposed to 'induced voltages'). As I suggested/asked before, would it perhaps be possible for you to connect some sort of 'load' (e.g. an old-fashioned filament lamp/bulb) between your multimeter probes and see if you can then still measure any of these (small) voltage differences?
Something like this:
I'll figure something out!Hmmm. Not much further forward, then.
Any comment in this discussion has to be qualified by "nothing is impossible", but I would have thought that if there were enough water sloshing around under the floorboards for significant amounts to get into a junction box, you would by now have water coming through the ceiling below - or, at least, evidence of the water leak on the ceiling.
I'm a bit confused by that. Although it would probably be necessary to rip up flooring to deal with any water leak that was detected, if his theory is that water in a JB is causing an (electrical) 'leak', I would have expected him to confirm (or dismiss) that possibility by undertaking Insulation Resistance tests on all the relevant circuits, which would not require any interference with the flooring.
