Thanks for all the advice guys. I've put it all back together minus the return from living room for distributing sky as dont do that now with sky q. Cannot get earth down to under stairs like I wanted so will probably get a bit of 6mm and a pipe clip and go to the pipe work by boiler.
Thanks.
I'd be much more cautious of just adding an earth because you've found 100v (AC?) to earth.
Right now it sounds like it's just floating on all your unearthed media gear common chassis ground & av screen & unlikely to be going anywhere (atm) hence why you can feel it & get that reading on a test meter, if you did have any gear with an earth that would pull it through that peice of gear.
Once you add an earth it is then 100v* going to earth. (10 or 20v would be nicer)
* If it is 100v, if it's rouge AC from a switch mode it could be something different to 50Hz (eg higher) so there's no guarantee a test meter will measure it accurately.
Before doing that earth, I'd check your media gear to try to establish you don't have a failing PSU (or 2) somewhere & if you do & it goes worse which it will, you'll have it belting through all your gear en route to that earth.
Old sky box's psu's are No.1 then old TVs then any old stb & even new but cheapo Chinese boxes like a cheap IPTV box with even cheaper SMPSU. Check gear regularly & avoid keeping old or used gear.
To earth or not to earth on media gear / systems has become a major headache (on single dwellings) not least because of issues like this - but neither is ideal, we've just gravitated to everything being double issolated / without an earth now but no one's thought it all out or what happens when lots of av equipment is all effectively connected together via aerial & sat leads AV leads wired lan etc & then stuff gets old & no longer at the spec it was new ?
Btw.. I think 50v is the max allowed, for safety re electric shock, but that's including the resistance path (you) so shouldn't be that but you could measure it (with you touching the rf amp meter between your other hand & the boiler . But thats for shock levels not av gear interference / damage so its just amusing to see what's left.
Oh, pipes might not always be earthed now because of the advent of plastic fittings. That whole bonding thing got in a mess several times with knee jerk lehislation based on one postmortem rather than national data.