Reverse Polarity

At the main cut out L should be on the fuse carrier side can confirm with a Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

LAmp/ meter will not work on a PME supply if the 'E' you use is (due to reversal) the live one.  In a well isolated location - like an upstairs maisonette fed by plastic water pipes or something, you could have the whole installation CPC alive and not feel very much, and the tester may show good when it isn't

The non contact probe may or may not work as well as you expect, depending on how much of an equipotential zone the building made - don't forget that the second terminal of the volt-stick is the capacitance to the local environment, augmented by that of the user.

I have heard of both L and N/E showing as live for a non-contact tester, but not seen it myself.

Mike

It could get reversed in several ways, common occurance is when the meter is changed

At the main cut out

At the meter

At the CU/DB

At the socket

Ways to check

At the main cut out L should be on the fuse carrier side can confirm with a Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

At the meter N should be the 2 middle cables can confirm with a Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

At the CU/DB Contact stick and/or GS38 to E and/or lamp meter L to E.  N will not light lamp or sound contact stick

At the socket use a 3 pole plug in tester or use MFT to test polarity

If there are connector blocks in the mix they are also a source where polarity can be reversed. 

I would like to think that the DNOs have a means of confirming correct polarity, but I have struggled to find anything online.

I would have thought in most cases simple inspection would be enough - when  Ls are cores and Ns are concentric - it's pretty obvious there's something wrong if someone tries to connect core to armour or vice versa. Easier to make a mistake with open wire overheads (but they don't usually serve PME installations) which really only leaves ABCs - I'm not sure if they have a foolproof way of distinguishing PENs from live conductors then (other than the number of 'ribs' in the insulation).

   - Andy.

It may not be the advertised process but a wire to any outdoor electrode of opportunity (water pipes, lamp post to the meter probe into the mud, to pry bar or larger screwdriver in the lawn) has been seen being used by the local chaps round here. That and the tip  of a knife to pinprick into the insulation of the cable and then a connection to the knife...

In tight situations when things feel off, folk get inventive quite quickly and SSE are no exception. To be fair the stabbed cable was taped up with self amalgamating tape afterwards, and replaced once the final repair was made.

Actually even the few mm of exposed metal on the  probe tips a digital volt meter makes a good enough "earth" to indicate a few more volts than expected, which is all that is needed to trigger the 'something's up' alert that leads to double checking, It may be an electrode resistance of 10kOhm but the meter still shows there may be dragons.

Mike

I see what you mean.

I would like to think that the DNOs have a means of confirming correct polarity, but I have struggled to find anything online.

Some installation testers have a single pole test built into them as well.

youtu.be/HyzlpD66EW0

Depends what you mean by Earth - short to the DNO's Earth terminal, yes. Connect to a local electrode - probably not - more likely a few amps flow....

In the OP's suggested case it's only a reversal of the L and PEN conductors - no short as such (unless there's bonding to extraneous-conductive-parts that are metallic though to another installation, where they're bonded to a correctly polarised supply from the same transformer, in which case, yes flash and bang again).

    - Andy.

I did consider that, but then also tried to envisage an extraneous conductive part free situation, perhaps a house with no metallic services... and in this situation could a PME Line/ PEN reversal remain on the installation supply, prior to installation energisation?

Surely if you earth the incoming live there will be a big flash and lots of smoke as the earth lead burns up also after all you would get current of hundreds of amps just briefly until your earthing and or bonding conductors burn up. I cannot imagine it's a situation that could last long

I wonder how well the single pole/non-contact voltage indicators would work in an installation  where main bonding connected the metallic structure of the building to the supply L (normally PEN, but reversed). If I understand correctly, they use stray capacitance between the user and the rest of the world to complete the circuit - but if the surrounding world is at 230V rather than 0V wouldn't we be back in the same situation as for conventional 2-pole testers?

   - Andy.