I have known my TV aerial lead to have enough potential on it to light my
neon screwdriver and just about feel it as a little nip touching it. It
was the latter that had me reaching for the neon screwdriver.
I had more than "a little nip" when I unplugged an aerial cable from a tuner
that was connected to my (earthed) PC, while touching the PC case with my
other hand. I eventually tracked it down to my TV which was on another leg
of the aerial cable (loft-mounted amplifier and splitter - unearthed). There
were a lot of culprits to check because my VCR was connected by phono cable
to my hifi, and all these devices were unearthed (double insulated).
When I measured the voltage on the screen of TV's aerial socket wrt ground,
it was about 130 V (!). There was evidently a large resistor, because when I
added a "human-sized" resistor where my body would have been (*) if I'd had
mains earth in one hand and aerial cable screen in the other, the voltage
dropped to about 50 V - still enough to give a fairly strong jolt when
you're not expecting it.
I added a wire from the earth pin of the amplifier to the screen of the
aerial cable (just one earth point, to avoid hum loops) to make sure the
TV's aerial/phono screen was grounded.
This was a modern TV - I bought it new in 2000 - so it wasn't one of those
ancient TVs with a live chassis. I was very underwhelmed with the reply I
got from Panasonic when I reported the problem: 130 V no-load voltage on a
part of the TV that the customer might touch, reducing to 50 V with a human
load, was not what I would regard as a safe design. I did check that the
plug was correctly wired, and that live and neutral hadn't got swapped.
(*) The shock was strong enough that I didn't want to repeat it, even as
part of the test!