Brian wrote:

While there, I also bought a simple continuity tester. With the power off, I
tested the continuity between both live and ground, and neutral and ground.

To my surprise, the continuity tester "chirped" - beeped briefly - and its
LED flashed briefly, before remaining silent. Continuity is normally
indicated by a steady beep and a lit LED.

There's plenty of ways to account for your 'chirp'. L-to-E first: any
appliances still plugged in to the ring with interference suppressors
will have capacitors placed L-to-E (and N-to-E, too). There'll be a
brief current flow as these charge up on testing. There's natural cable
capacitance too - those L and E conductors run next to each other with
nobbut a mil or of PVC between 'em for tens of metres, don't they...

N-to-E not only has those capacitances, but they're actually bonded
together in the UK. That bond may be close as the supplier's side of
your fusebox if you have a TN-C-S (wot we old farts call PME)
installation, or as far away as the local substation for TN-S or TT.
Since you only got a chirp, you prolly don't have PME, and have the
'usual' small voltage offset between your N and local E.

.............. I found out that my ring main was incomplete and
traced the wire to a socket box in the kitchen, where a N wire was out; this
socket box had been fitted by "professional" kitchen fitters as supplied by
MFI.

The scare quotes seem entirely appropriate; just because you pay more
than peanuts doesn't mean you don't get monkeys (who themselves may well
see only peanuts - after all, someone's got to pay for the salesdroid's
new Jag. D-i-y by a conscientious householder is notably safer than a
tradesman who just 'turns their hands to a bit of leccy work'...

Stefek