I’m slumming it with 6mm2 and the supplies works great 
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The phrase, “Keep it simple stupid” springs to mind (them not you that is)
Earth loop impedance faults spring to mind also with all those earthing points dotted around your house. I assume you only have a single (single phase) supply after all.
10mm T&E is not exactly flexible and easy to work with, the main challenge is finding a socket that is designed for that sort of cable, most aren’t as they don’t need to be connected to 10mm cables by design (induction oven or electric shower maybe but they don’t use sockets!).
So make sure you source and allow him to verify sockets that are known to be designed specifically to accommodate correctly and safely 10mm cables. MCRU or Furutech are good places to start in that respect.
The standard MK double unswitched socket that is commonly recommended will take 10mm cables. At a push it will take two of them in one connection terminal, allowing more than one socket to be joined together if you want them, although it wouldn’t be entirely unreasonable of an electrician to refuse to do this given the tight fit, not only of the connections, but of the excess cable that needs to be pushed into the back box when fixing the socket in place.
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You should go ahead with their plan….the forum needs the knowledge😂
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That’s crazy… Even for Japan. What you describe is surely excessive. You just need what you asked for - a separate feed for your Hifi, with its own earth. Copper wire will do fine…!! Plain trunking, nothing fancy needed.
Hope you can get your contractor(s) under control… 
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Thanks for the replies…I’ll update accordingly👍🏻
When I had a go at them (and I really nailed them to the proverbial wall), three of the four people sitting opposite me were all glassy eyed and trying to not cry. They are fully aware they screwed up.
Today, they were apologizing and I told them, “the second the electrician didn’t push back and tell me I was crazy like I’m used to, and instead said they were also an audiophile, I knew something was very wrong.”
It’s being sorted now via me stepping in and micromanaging every purchase order and wiring diagram. I really only have two choices: Learn to laugh it off; or have a stroke.
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Me too, though if going to the effort of installing dedicated mains, I thoroughly recommend the installation of a specialist breaker and RCD.
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Update 1 - I received a message from my sparky last night to say he had completed his tests and confirmed he is happy to use 10mm2 cable as, in his words, ‘it fitted into the double un-switched socket with no issues’.
Just waiting for the quote and when the job can be done. Looking at others experiences would I be right in thinking around £500-£600?
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It really depends in how long-it will him and how much cable etc
I paid around that price in 2018 including a long run (30m) or cable from one side of the house to the other and about 5 hours in all of the electricians time. That looks a good quote, considering where things are in general with prices in 2023 !
10mm will fit in most UK sockets from all that I’ve read - but you cannot make a ring with it (as you’re aware) and the primary problem is that it’s so stiff, even with the outer-sheathing removed.
One aspect is the pattress/wall-box to be used e.g. if you haven’t got adequate wall depth (pretty much double-skin brick) to accommodate a back box (if you coming through a wall?), then they’ll be looking at surface mounting(?), which very likely means have a deep surface mounted plastic box – FYI, my pattress boxes inc socket top sit ~60mm from wall. Add a plug top and you might be 75mm proud of the wall line.
Us hi-fi nuts may be OK with this but others…?
One other thing to be clear with sparky on is height. as it’s my understanding that sockets should really be at hip height nowadays, unlike the old practice of locating them just above the skirting line. Of course, a bit of planning with any kit support helps.
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Be careful of one thing. If you are using bog standard UK mains sockets like M&K ones you’ll be fine. If you present your sparky with audiophile ones he’s not tested, you might be in for a problem. Popular Furutech ones only open clamps to 8.3mm.
Yuck! For my SWA 10mm cable, we agreed a deeper wall box of 40mm IIRC - worked fine, and looks great
James…further to my message. Is that a seal on the Henley Block?
The technician who fitted my replacement smart meter put the seal on the Henley block. It’s on the customer side of the meter so not DNO responsibility and no reason really for it to be there.
She was pretty thorough though and I think added it as I have no isolation switch between meter and Henley block. Perhaps as an extra reminder to anyone in future who may be working ‘live’ on the block.
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James, how long are the meter tails?
Is the audio CU the other side of the meter box wall, or some distance away?
Hi Debs - both consumer units are in the garage on the other side of the wall behind the meter cabinet so it’s a run of approx 2.5m for the tails from the Henley block.
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