In uk.d-i-y, Adrian Simpson wrote:

Today, the power stayed on, so I got a proper meal tonight :-)

Good - can't have you Blaining out on us through lack of food ;-)

The main RCD was fitted new last December (the previous one had a broken
casing, so it was changed on safety grounds) 30mA trip, 80A capacity.
It is situated on the tails between the meter and the consumer unit, so
only has Live/Neutral connections to it. As the house is a low
occupancy two bed bungalow, then the total consumption is not that high
.................................................. .... Not sure why the
earthing is done the way it is, I'm not rural, but I am on the edge of
town. So far as I can tell, none of my neighbours has earthing
arrangement that I have, but I doubt that any of them could tell me what
they do have. The good news is that at least I do have an earth now (it
was not connected up when I moved in).

OK, this gives us more information to work with. Your whole-house RCD
is definitely a Modern current-operated one, then. It's no longer thought
Good Practice to fit a single 30mA RCD as a whole-house fitment, actually:
split-load arrangements which leave the lights on and put the more-likely-
to-have-benign-leakage circuits (immersions and cookers) on the non-RCD
side, and the more-likely-to-fault-with-danger-to-human-life circuits
- especially sockets rings "likely" to be used to supply tools used
outside the house - on the RCD side. So whoever fitted the 80A/30mA trip
(you? a sparks?) was following last decade's accepted practice ;-)

IF you're confident in your own competence, you could go split-load at
minimal kit cost by running the tails which now go to the RCD into a
Henley block (fat-arse junction box ;-) from which you'd run tails into
the existing RCD-and-on-to-current-CU, and also out to a new small CU
with say 6 or 8 non-RCD-protected ways, for your lights, cooker, and
immersion/CH circuits. This is *only* safe if you have a decent earth
for these non-RCD circuits, mind! If you're not sure of that, you really
should get a real sparks in. S/he might end up recommending you fit a
time-delayed 100mA-trip RCD to give short enough disconnection times
if your existing earth isn't low resistance enough; downstream of that
you could (and should) still run a split-load arrangement, whether in
a single new CU or the Henley-block-and-two-CUs stylie outlined above.
The difference in both trip ratings and time-to-disconnect between the
100mA time-delayed trip and the 30mA faster-acting trip preserves good
"discrimination", i.e. an earth leakage fault on the 30mA side should
make that trip, and that trip only, disconnect, leaving power on to
your lights and other circuits.

Hope that helps (and thanks for bottom-posting; now move further up
the style scale by trimming the post you're replying to more aggressively
- OK? :-) - Stefek