There are a series of things that can be wrong both with the hardware you plug in and with the plug itself. Things can straight up be wired in the wrong order, grounding can be done incorrectly so there's more than one path to ground which among other things causes there to be a voltage difference between the neutral wire and the ground wire, corrosion or bad connections can cause similar issues.

The first cheap test you can do is buy one of these plug testers that diagnose some of the more direct problems you could be having for about £10, don't necessarily buy the one I linked, but do a little research and pick something that seems right.

https://www.amazon.co.uk/QUILLE-Socket-Display-Neutral-Testi...

If you're having those kinds of problems, it wouldn't hurt to contact a local electrician and quickly describe the issue and ask what it would cost to diagnose.

I'm not familiar with the UK wiring standards. However an easy first step that I would imagine also applies there is losing the bonding jumper between neutral and ground at the main circuit breaker panel.

In Canada and USA with our split phase residential system a decent next step is to overload 1 phase causing the neutral to start drifting from 0V.

In the UK with single phase supply I imagine the next best thing would be to also break the neutral return to the pole which should generate at least 100V on the neutral (and also stop all appliances from working), fortunately for you (I think) the UK mandates GFCIs (RCDs) on all residential circuits which would also prevent that from actually killing you.

In summary, I'm going to guess that touching neutral in the UK is a healthier past time then it is in the US or CA. Still not healthy, but at least healthier.

Sure, but DC relative to what? Can't be ground since that connection isn't there, so that leaves neutral.

I've got half an alligator clip on my workbench, the other half disappeared when I connected it to the floating ground of a 5VDC system. It just so happens the ground was floating on top of 120VAC. The ATmega didn't care, it only ever saw 5V between its Vcc and Vee, however once I made the mistaken of connecting its "ground" to an actual ground sparks flew.