Mike

It looks in good condition & you have 200 years of evidence that it's adequate. What has changed over the years is that current standards require the timber to flex (sag) much less under load than would have been acceptable in the past; that's normally more a risk of cracks along plasterboard joints, rather than one of structural stability. I doubt the the BCO will raise it as an issue, but if they do, then you'll need that SE. If I were drawing the plans they'd just have a note saying something like "existing lath & plaster removed & replaced with plasterboard". And something similar if you're planning to replace the tiles externally / add additional insulation, etc.

No, it's never a problem that I've come across when the timbers are in good order. If everything had to comply with the latest Regs then you'd be demolishing the lot! It just needs to be safe and, if there's any doubt about that, then you'd need a Structural Engineer's involvement.

Wall ties are supposed to slope gently towards the outer leaf...

No, but you may be able to do it. The use of lime lies outside the current British Standards, so it would be down to your structural engineer to make an assessment of suitability. However the NHBC Foundation have produced a paper on the subject, which may help - The use of lime-based mortars in new build (https://www.nhbc.co.uk/binaries/content/assets/nhbc/foundation/the-use-of-lime-based-mortars-in-new-build.pdf) which does say that "The data available indicates that single skin brickwork or blockwork masonry constructed with lime-based mortars quickly develops sufficient resistance to vertical loads, but that it has less resistance to lateral loads at an early age and so consideration needs to be given to this at the design stage."

FWIW, I avoid using glassfibre now; it's not much fun to work with, even with a respirator & gloves.

I've used the 3M 6200 half mask for years - not sure if this is my 2nd or 3rd (the others wore out) - similar to the Dewalt one. I used a couple of other brands in the past, but ended up throwing them because their proprietary filters became unavailable. That's not been a problem with 3M. For dust, I use the 2135 filters; a pack of 10 pairs will last me for months or longer, depending on the dust levels.

From experience hemp is good to work with but really tough to cut - a toothed blade is impossible. If you're doing a small quantity, then you can get away with the Bacho Profcut PC-22-INS insulation saw, though it works works better with normal insulation (EPS, XPS, etc). For larger quantities of hemp or woodfibre, it's essential to invest in an electric saw with wavy-edged blades, which make it almost as easy as cutting butter. I only know of 2, but there must be others: Bosch Professional GFZ 16-35 AC + the TF350WM blades (I got through 2 pairs) - demo if you look for the video at https://www.bosch-professional.com/fr/fr/lame-de-scie-tandem-pro-fibre-insulation-tf350wm-3053403-ocs-ac/. Festool 577231 18V cordless You may pick one up on eBay, as I did.

You live in France. I don't remember them being that bad last time I visited the UK. Though it's been a long time since I made it to Cornwall...

Overall, remarkably accurate. Starting with all that 'clutter' in the fist section - all now available on your smartphone. They're partly right - you can recharge that smartphone wirelessly. Thankfully! And fashions have improved too.

At that thickness even the most expensive insulant won't do much; in fact it would be more-or-less decorative as it would be bypassed by the outer skin sitting on top of the beam (and maybe by the patio door). You may be able to build the brickwork off Armatherm (ask them), but if the brick is already in place there's no good solution. Other than to dismantle it it and approach it differently (and claim the cost back from the structural engineer who designed it?)

I've done similar, though using a plastic angle to keep them straight.

This will give you a clue: https://www.researchgate.net/figure/sopleths-for-growth-of-various-fungus-species-and-the-lowest-isopleth-for-mould-LIM-0_fig1_272886603

+1 for blown EPS. The silver / grey ones provide somewhat better insulation than the plain white.

If under a warm / hot shower I doubt MVHR on boost would give you any discomfort in an open room. There's scope for some consumer testing here - just don't post the photos :)

Zehnder's recommendation is that it should be close to, but not directly over, the shower. No reason given, but my guess is that it's not about the functioning of the MVHR unit, but rather that the air being drawn past the person showering could, in some circumstances, feel uncomfortably cool. For example if you don't have a good shower screen & door in place.