Fred wrote:

Connect the CU tails and the T&E into the switch fuse if it will fit?
I had not thought of that.

Not the 6 mm^2 T&E directly (into SF1) since you're still fused at 60 or
100 A at that point - but you might get 16 mm^2 single sheathed or T&E
in, for the short run to SF2. It depends on what make and size SF1 is,
but 100 A stuff often has 50 mm^2 terminal capacity, which would be
sufficient. Check out the actual available wiring space, as well as
terminal capacity.

(I presume that 6181Y means a tail).

Yes "meter tail type cable" readily available in cut lengths in 16 and
25 mm^2 for tails etc., but also available in the full range of sizes:
http://www.tlc-direct.co.uk/Main_Ind...New/index.html

Whoa indeed. Another refinement that I had missed in my initial
thoughts. I presume I could run single sheathed cable from the Henley
block to SF2 and the T&E from the other side of SF2 which would solve
my tail to T&E transition problem.

Exactly so.

I must confess I have not seen 30A switch fuses; I thought they were
80A or 100A. I will have to pop to a electrical trade counter.

It's a 1-way consumer unit really, e.g.:
http://www.tlc-direct.co.uk/Products/WY106.html
(but fit a 30 A cartridge fuse, not an MCB, as that will give you better
downstream fault discrimination).

--
Andy