[LoneWolf (OP)]

Evan_au when I said ~80mV it should have been ~80V/m my mistake. I don't understand what's caused it to jump up to  261V/m. I have juatvdone some problem solving, I left the detector on the matt (it was beeping) and turned the electricity off at the consumer unit and the beeping stopped, the readout was 0V/m. So something is leaking to earth. I have a number of surge protectors, could it be them? Also, if I turn my hot water on (conventional system) the TV downstairs goes off for a second. Wonder if its that.

[alancalverd]

Almost certainly a significant "earth" voltage, possibly a wiring fault. Has the property been extended, rewired, or acquired some new high-power kit like a jacuzzi?  I recall a client complaining that he felt a "tingle"  walking from his swimming pool to his new hot tub: I found the two "earth bonds" to be 50VAC apart.

So back to my earlier suggestion: bash an earth spike into damp soil and measure the voltage between the planet and your mains earth. Should be less than 5V AC or DC. If not, get an electrician to investigate. Likewise, as you now have a long piece of wire, check the voltage and continuity between the earth pins of your mains sockets in adjacent rooms.

Surge protectors and interference suppressors can leak significant current to earth but the bonding  between adjacent rooms  and from any room or installed device to the incoming main earth reference terminal should be better than 0.2 ohm.
 

[evan_au]

a 50 Hz field strength exceeding 1.4 V V/m will produce a sensory effect

Is this a typo of some kind?

When I pick up a 1.5V battery across the terminals, I don't feel a tingle - and that is through a 0Ω circuit.
- The reason is that my skin has a breakdown voltage of over 12V (provided I don't have any cuts)

However, 1.4V/m through air has a series impedance of 1 MΩ or so; I don't see how that could produce a "sensory effect"?
- Could you mean 1.4kV/m? (1.4MV/m would have a hair-raising effect, often seen in science museums!)

● the electric field induced inside the body is considerably smaller than the external electric field, e.g., five to six orders of magnitude at 50 – 60 Hz;
● for a given external electric field, the strongest fields are induced when the human body is in perfect contact with the ground through the feet (electrically grounded), and the weakest induced fields are for the body insulated from the ground (in “free space”)

And...

●Thresholds for direct perception by the most sensitive 10% of volunteers at 50 – 60 Hz ranged between 2 and 5 kV/m
●However, peripheral nerve stimulation induced during volunteer exposure to the switched gradient magnetic fields of magnetic resonance (MR) systems suggested that the threshold for perception may be as low as about 2V/m
●The threshold for induced electric field strengths in the retina has been estimated to lie between about 50 and 100
mV/m at 20 Hz

So here we have an enormous range of potential effects....
- For 50Hz electric fields in the home (through air), we are talking about kV/m
- If your home is within the extremely strong magnetic field of an MRI, and subjected to loud audible noises and radio-frequency fields, 2V/m may be detectable
- At the other extreme, your retina (essentially an analogue detector) can be fooled by fields as low as 100mV in the right frequency range (but external electric fields would be attenuated by several orders of magnitude because the retina is within the conductive fluid of your body). Magnetic fields in the mT range can also produce visual effects, and these aren't strongly attenuated by the body. 

Overall, external electric field recommendations for public exposure to 50Hz voltages (through air) are < 5kV/m (and higher for workplace exposure)
See: http://www.icnirp.org/cms/upload/publications/ICNIRPLFgdl.pdf

[Bored chemist]

The reason is that my skin has a breakdown voltage of over 12V

No it hasn't.
A half decent meter will measure the current through your fingers driven by  a 1.5  volt battery.
The current voltage curve probably isn't close to linear.

When I pick up a 1.5V battery across the terminals,

Did you see the bit about 50Hz?
Capacitive coupling starts to become important.
At higher frequencies you start acting like a radio antenna.
And that's where those field strengths they quote apply.

[alancalverd]

IIRC the IEC 60601 low-frequency model for a human being  is 1kΩ in parallel with 1μF with a maximum permissible current of 5 mA from hand to hand. This presumes intimate contact with saline-wet hands (it's the medical equipment safety standard). In my civilian capacity as a double-bass player, however, the skin on my fingers is so hard and dry that I don't always notice 100V DC.

The CEFWR sensory effect ELVs are for electric fields inside the head. Until Alzheimer takes over completely,  I think the contents of my skull are a lot more conductive than my fingertips, and my optic nerves are carrying microvolt signals.