In message , John Rumm
writes
chris French wrote:

John, you suggested borrowing an insulation tester - if I had any
idea where to borrow one I might, but TBH this does seem to have been
a one off, the rest of what I've seen generally seems ok

I have one in SE Essex if that is any use... Failing that a hire shop
may be able to help.

Thanks, but we are in the middle of Cambridgeshire. I might investigate
hire options.

One, to (presumably - I need to remove the base of an old climbing
plant to find it) a buried earth rod, the second looks older -
connects to an external copper pipe. This looks like an old gas pipe.

Using a gas pipe was not uncommon. I used to have one in my house which
just used the gas pipe as a main earth. The danger is that these days
they may end up replacing large swathes of pipe with plastic and this
can interfere with the operation of your earthing.

It's unlikely this bit of pipe would get replaced with plastic (more
like just removed all together), but anyway, we have a proper earth
rod.

Anyway sorting out the meter/CU area has been on the job list for a
while. It's probably up to 40 years old, the main CU is chockerblock
and there is the typical hotpotch of extra switch fuses etc. A new
bigger CU, a main RCD, sorting out the main earth bonding etc.
Probably starting with replacing the VOELCB with an RCD to give more
space for the new CU, partly because that can go elsewhere on the
mounting board - replacing a great big F-off metal main switch -
there presumably because the house has a 3 phase supply. Though only
1 phase is used.

In circumstances like that it can often work out simpler to install two
CUs fed via split tails from a main switch. You can stick an ordinary
100mA trip RCD in one for all the lights and other circuits that do not
need direct contact protection, and then have a 30mA trip RCD in a
second CU for the power circuits. Often works out cheaper than having a
£100 time delayed RCD cascaded in the same CU as the smaller threshold one.

Ahh yes, that's a good suggestion, thanks.
--
Chris French