Some feedback on how it all went:

Befo 60A cutout. Dual tariff meter, 2 old Wylex wired fused CU's
(one with a comedy home-made wooden backbox), electromechanical time
clock feeding 3rd (comedy wired) CU for off-peak, Henley block and
jumble of incomer wires etc. 2 Different comedy backboards, hanging off
wall at comedy angle.

After: New 100A cutout. Wylex 12 way, split load CU (from Screwfix,
incl 10 free double sockets - bargain!). Minimal install whilst
converting an old chapel, CU on wall, 2 double sockets abutting it. New
single traiff digimeter (smaller than a double socket).

Arrangements: Start by calling my supplier, explain what's wanted, they
send letter with (wrong) number for EDF. Call EDF, explain what's
wanted, they send quote. Pay quote for £323 (ouch). Arrange their
surveyeor to visit. 5 minutes on site, no problems, also agrees
reduction in charges to £240 - and specifies 25sqmm tails, 16sqmm main
bond,10sqmm secondary bond. Letter from EDF detailing what I have to do
(install new CU, arrange supplier to reconnect meter). Call to EDF to
set this in motion.Call from EDF to arrange date. I call supplier to
arrange same-day reconnect.

On site: EDF have giggle at old installation. Set up new backboard,
mount new cut-out, snip through live incomers (nice demo of good
live-cable working practices) and reconnect to new cut out. Fuse left
with me to await meter company. (They also offer to reconnect old
meter, but I pass on this).

Meter company engineer turns up. Tells me meter swap is scheduled, not
reconnect - but says he will do it anyway. All connected up. Dead.
Whoops - engineer still has fuse in hand- had forgotten to insert it!
Fuse inserted - still dead. Whip off CU cover - one of the tails has
pulled out! Major whoops - my fault - I hadn't appreciated that meter
tails give quite a bit - but only when tightened down really hard!
Reconnected - all good. Uses plug in polarity tester. I make up a small
offcut of oak for his baby-gate at home. Everyone happy.

I finally test RCD and check earth loop impedance on new installation.

None of the engineers looked at CU test certifcate (download from IEE
website, borrow mate's 16th ed. tester - thanks Ben, and very rare
occasion to actually sign something using letters after my name) -
though installation looked "professional" (used to be electronics
engineer) - er - apart from the comedy pull-out meter tail - which is a
pretty embarassing mistake to make.

Overall - it's the usual story of clueless phone-wallers and very
capable engineers on the ground. I may have a chat with EDF about that
£240 charge - the engineers only needed to spent 30 minutes on site.