In uk.d-i-y, Al wrote:
I have a 30s house with some rubber-coated wiring.
Before replacing this, I'm going to put in a new consumer unit.
Before doing that, I'd like to ask a couple of questions.

My problem:
There is no consumer fuse - tails go straight from the supply cable to
the meter.
From the meter, the tails go to a small junction box (would this be a
"Henley" block?).
Tails then go from the junction box to the consumer unit.
My plan is to carefully remove the old consumer unit tails from the
live terminals using an insulated screwdriver, then fit new consumer
unit and new tails.

Eeeeeeek! You (or I) *really* don't want to be doing that. "Live working"
is something to train for carefully, needing planning ("what if the wire
springs back, what will it touch") and well-tested tools and kit (VDE-rated
insulation, thick insulating mat). It's a *really* *really* poor idea to
improvise. Even more so on an installation you're already saying is
(to use a technical term of art) crap.

My other problem:
The current wiring would not pass any sort of inspection, and I'm not
expecting to finish the rewiring very soon.

Rather than a "big bang" changeover, many competent d-i-y'ers do the
"new CU" thing by running brand new wiring to a nice shiney new CU alongside
the old one, and feed the new CU's incomer from a suitable way in the old
one (30A or 40A rated) - diversity-for-real is your friend here - to allow
new and old circuits to both run during the week or five it takes to
do the job in evenings/weekends, while having power for joist-drilling
and the like!

But if you really have 60-yr-old rubber-covered cable, you're likely to
find it breaking off the cable as soon as you wiggle it even a bit. Are
you sure you can't scrape up the cash to do something safer - maybe
run new circuits for one or two "essential" power rings and lighting,
wired in to a lots-of-room-for-future-circuits new CU, then get a friendly
local electrician to connect it up (and cast an eye over your earthing
arrangements), leaving you to put in further circuits at your leisure?
I'd really not want to be living in, or responsible for, a house with
the wiring in the state you suggest...

Q1: Who owns the junction box?
It is after the meter, but is sealed with wire and (old looking) lead
crimps. That might mean something official, or might be to discourage
me from the above dangerous manouver.

It's really quite massively unlikely that you don't have a supply fuse
(conceivable, yes, but barely so); perhaps this Junction Box is indeed
a supply fuse and neutral link? How deep (front-to-back) is this
mysterious Box? Have you looked for a supply fuse further back from
the supply cable? (At this age I'd expect the supply cable to be a
tar-impregnated lead-sheathed thing: are you saying the inner conductors
emerge from that directly into the meter?) Maybe there's a supply fuse
further back, possibly at a previous meter location?

Q2: What exactly is inside the junction box?
Bakelite box, about 4" x 3". The meter tails enter on the bottom-right
one in front of the other (ie in a plane perpendicular to the wall)
and the consumer unit tails exit on the bottom-left, similarly one in
front of the other.

I've guessed at it being a supply fuse, incorrectly positioned beyond
the meter; but it sounds a bit small for that - and even in the 30s few
sparkies would muddle them up this way - so it could indeed be an
old Henley block (maybe put in when replacing a bunch of ancient-style
fuseswitches with whatever CU-substitute you now have... but haven't
had a chance to describe...)

Let me discourage you again from trying to keep this installation
struggling on: better to put up with a pain in the cash flow and
running with fewer, but safe, circuits for a while, than disturb the
old perished stuff which (from personal experience) starts to flake
off most worryingly when disturbed.

HTH, Stefek