Roundtuit

I packed a load of offcuts into the space under and around the bath. Theoretically, the bath water may stay warmer longer. Practically, I've kicked the can along the road for a few years. Win-win!

You can't see the side walls properly, but you can see the tiles. I'd expect to see flashing over the tiles, but maybe there's some sort of tray underneath?

My first observation is that they haven't used the ventilation system as specified, and secondly, there doesn't appear to be any flashings on the side walls which seems odd. Have you had the conversation with the contractor to ask why they deviated from the drawings?

I forget the detail, but someone locally installed 6ft electric gates within about 2m of the highway. They were caught out and had to apply for retrospective permission. They successfully argued that the gates could be operated by remote control on the approach so that no road obstruction would occur. Utter bull$hit, but they got it passed...

Yes. That's what self-building does to a previously rational person though. The big question for me is: are they stainless steel to avoid rust streaks on the render in 20 years time?

Years ago we where having some walls re-skimmed after damp proofing work in a 200 year old rural end-of-terrace house. I floated the idea of a 'rustic' finish, and the plaster refused without hesitation: "There's enough character in 'ere without f***ing the plastering up". 😆

Has the BCO not indicated what would be acceptable? Maybe have a look at metal galvanised stud systems? Might be a bit more expensive, but for a small area wouldn't break the bank.

They're for tying a brick skin to a timber frame during construction, so not really suited to your application IMO. You'll need to return the stud wall to the brick wall (where you have circled blue) to close the cavity, so use a strip of dpm between the timber and brickwork. That should stiffen your stud wall up enough to use maybe one intermediate bracket, and finish off by using the window board fixed to both inner and outer skin.

If you want to sell at some point, a surveyor might want to look up there. I can't really envisage loft access not being a good idea.

For good measure, I'd also cut the concrete/paving slabs back by 6 inches adjacent to the brickwork and fill with gravel to reduce rain splash.

My advice is to take on board whatever @craig suggests. Unless your agreement with the installer included improving building fabric to mitigate existing cold-bridging, then you only have some minor snagging issues that you could probably have resolved yourself with some expanding foam and sealant in the time taken to craft your comprehensive and eloquent posts!

I was reluctant to pay someone to do something I could do myself; did one ceiling with a roller and realised how long it was going to take to paint the whole house... Painters are not that expensive and come with all the kit 😉

The old classic: lt is easy; it's like riding a bike, except the bike is on fire, you're on fire, and everything is on fire because you're in hell...

Less plot and professional fees etc...? Any indication of plot costs in your catchment area would be helpful, and how hands-on you plan to be?

Is the 3 inches the full depth of the rafter? If so, I'd be cautious of hanging any additional weight off 75mm rafters, and be looking for a solution that added strength not just extra load I think.