thats a voltjigger, every house has one big houses will have more than one, excluding the fuse box that is marking where all the electrical wires of that room and possibly another room cross over, it means you cant screw anything into tjhat wall becasue you will hit a wire.

A Voltjigger? Never heard of it. You winding me up or what?

me...no.

Government probe?

Voltjigger, that's fantastic, LMAO.

From the looks of it and without seeing the wiring i would say that is an old style Flex outlet, hence the cable gland just visible through the hole (Ie you would have something fused back on the consumer unit like a boiler rather than having to run cable on the surface).

As to what it is connected to I would hate to think.
It is also possible that it is the end of a spur off your ring main, in which case unless you know how many outlets are on the ring and the total Ampage don't go trying to wire anything in there.

All in all get an electrician to have a look, if it turns out good you have the means in place to hang a plasma screen with no trailing wires.

Now that explanation makes more sense than a Voltjigger! Plasma screen sounds like a plan Jeremy.

Sorry Jeremy but i dont think you know what you're on about!

Isn't A Jigger a tool for measureing alcoholic ingredients. ;)

No Wonder I have got one then! Mine doesn't seem to be working very well though.
Maybe it's too high up the wall to work properly!