Mr Punter

This type of unit MUST be installed and commissioned by a legally certified F-gas installer.

And while you are doing this you could look at modifying or replacing the first floor cills. It is difficult to chase out cement mortar from soft bricks without damage. Do some research on what you want.

So, house > IC1 (picking up house, dry) > IC2 (inspection only, clear flowing water) > off somewhere else? Is the water meter showing any flow? When you flush a WC do you see the flush in both ICs?

You don't need a waste pipe behind the machine. Plumb it into the sink waste and no big plastic pipe to worry about. No upstand pipe needed as it uses the sink trap. Very much a standard way to do this.

Everything in the sink cupboard. Be aware that you cannot always change the handing of the porthole doors, just the furniture doors. You will need to take a decent chunk out of the middle support panel. For electrics you either need 2 sockets on the inside side of the sink unit or trailing socket under the plinth. Leave the plugs on the appliances for warranty purposes.

Can you insulate the whole sloped area between the rafters with PIR with a thin sheet under? It may be simpler to get rid of the knee walls to get access and put them back after.

If there is crack control breaks in the slab you will need to follow these in the tiles. If not, you should be OK with nothing.

You don't need consent from the owner but if they are unknown you will need to demonstrate to the planners that you have made reasonable attempts to locate them, such as a notice in the local paper, a sign displayed on the site and contact with neighbouring owners.

If you go with semi basement ICF you will need as a minimum type C waterproofing, which involves a profiled drainage sheet on the walls and floor, a drainage channel formed in the floor perimeter, a sump with a high level alarm end a pump. You also have to consider where you locate insulation and how you deal with drainage. Warranty providers may suck air through their teeth. Far better, if the site allows, change the profile of the land and have your building above ground, even if you need some retaining structures in the garden / drive.

Ronan point was built with sectional structural slabs of concrete for walls and floors. I understood the building in the OP was steel framed.

You can get retarder admix but too late now it is on the wall!

At least the shares are quick, cheap and simple to sell and purchase. Land and property is not any of these.

The samples are really annoying and hard to store and dispose of. I think a photo of a panel gives a good idea. Try an image search for Rural Multi Classic Brick and see what looks good. https://www.jewson.co.uk/p/classic-brick-rural-multi-imperial-68mm-BRCBC009

I think you need to get in touch with the people who did the tests and ask why they decided on 1.8m.

You can get double sided butyl tape for sticking DPM / DPC / radon membranes. Use that. Don't overthink. This is just to comply with regs. Anything built before the 1990s has nothing at all, so that is at least 85% of all housing. Use youtube to have a practice doing the corners. It may help if you ever do flat roof membrane in future.