"ARWadsworth" wrote in message
...

A sealed Henley block? They do exist but I am with Chris on this
one.

I'm not. The description provided...

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.

.... is clearly a bog-standard 2-pole Henley block. In the past (pre the
coming of the consumer unit concept) they were often provided by the supply
co. in order to connect additional fuseboxes and were routinely sealed,
being part of the suppliers' works.

Any chance of a photo of your supply Al?

Just what I was thinking. The main fuse(s) must be there somewhere and my
guess is that it will turn out to be a pre-1937 cut-out with a fused
neutral. Sometimes these had really tiny fuses in - 15A or so!

If this is the case the cut-out, and just about everything else on the
supplier's side is likely to be seriously undersized - so any hope of just
connecting in to the block sounds a bit optimistic. The correct procedure
(AIUI & IME) is to consult with the supplier (the supply network operator)
regarding the need for upgrading of their side [1], then complete your new
installation - which must include inspection and testing and completion of
an electrical installation certificate to BS 7671. You can then call them
out to do their side and connect your new tails at the same time. Now that
the ESQC regulations are in force you won't get connected without the
certificate; the days when 'the board' would do the testing for you are long
since gone. But YMMV; it can depend on who you get.

[1] This is a good time to consider earthing arrangements, and check what
will be offered. If the service cable has to be replaced you'll almost
certainly be offered PME (TN-C-S) so you can base your new design on Ze =
0.35 ohm. If an older cable is retained then TN-S conditions may obtain,
with Ze = 0.8 ohm.

--
Andy