Redbeard

I'd go with your gut feeling, then, and go for LA.

It will probably be clear that my post above should have said ''Then repair the flashing''. I left it too late to edit.

No, but my general experience of LA vs private BC has been that LABC are more thorough, though to be fair, see-very-little 'fly-bys' can be common to both, and the use of photographic evidence is, in my view, at very least a mixed 'blessing'.

If the flashing remains intact then it seems to me the top (although not where it should be) will not leak. Do you think I am correct in this? If so... cut pieces of 45x45 PSE to fit in each 'bay', fixed to the ledger-plate at the top to prevent 'droop', then make 'tingles' (glorified 'slate straps') to hold the bottom of thhe sheets to stop them falling further. So, 'downstand' down the face of the wall-plate, horizontally across the wall-plate towards the lower end of the poly sheets, then an upstand holding the sheet in place, with a drip-end on it (a little - 15mm? - 'turn-down). Or maybe I haven't read the OP well enough... Yes, I hadn't read the OP well enough!! I see the flashing tape is damaged. Scaffold planks across the lot to support you and spread the (otherwise) 'point-loads'. I would suggest do this *after* you have put the restraint straps on the bottom. The repair the flashing. (Assuming it is 'flashband' perhaps take the opportunity to do in lead - don't forget the patination oil. Unless you feel you have to I don't think there is any need to hammer the sheets back up as you suggest. I think my 'remedials' suggestion sorts that.

I suspect the more important Q is how far down will his wall start? If it is genuinely 3m tall it will have to start in a trench probably 900 (all right, maybe only 600, but I am Not A Structural Engineer) deeper even than that. If he does not start below the level of your land then, as far as I can see, it may be able to behave like a snowplough over the years, slowly moving his garden towards yours! But I may be wrong!...

I have had many more problems with nuisance tripping with my 3 linked mains-fed alarms than with any battery alarm over 30+ years. I now use the 10-year sealed ones. Mains-fed was a stipulation of BCO but they did not have to live with the jolly things going off at random times. We have not-linked but functional alarms in the relevant areas which do not nuisance-trip.

That's incredibly well camouflaged!

I wondered if maybe you'd got too much caulk. That won't rough up without looking like it's been attacked by a magpie. I cannot explain why the top and sides peeled. You mention plasterboard. Was it joint-filled and then paint straight on the plasterboard? That should adhere OK, but if it was skimmed it could have been over -'polished' - again, potential poor adhesion. Come to think of it, if it is just joint-filled, that may account for your top and sides if the joint filler was over-trowelled. Have to say I have never had adhesion probs on tape and fill pl'bd. I have no idea bout the colours of masking tape I'm afraid - all a bit hi-tech for me! It was (and is) all buff for me!

It looks like just inadequate adhesion/'keying' of the pink paint to the white under-layer (what is it?). Can I guess that you have maybe run the skirting paint (a top-coat) onto the wall? If this is the case then it's your reason; gloss (or satin or whatever) is a top coat and not designed to 'hold' another coat on top. Fine sandpaper, rough it up, preferably use an undercoat, then gloss/satin on top. (Alternatively I may have misunderstood the issue, in which case please tell me where I have 'mis-assumed' and correct me).

+1 to @Iceverge's a/t tape. Unless there is a solid layer behind the membrane I do not see how a squirt of sealant can be relied on to actually seal the hole. (And, come to think about it, if there is a solid layer you can't get to the hole itself anyway (to tape or to 'squirt' - You'd just have to squirt sealant down the batten-hole and hope. All a bit 'loose', perhaps.

Is this habitable space or a garage/outbuilding? And I assume the membrane is a breathable membrane to go under tiles or slates, not a 'flat roof' membrane such as EPDM or felt. Can you confirm? If it is to be battened and tiled or slated I'd say get the joiner to staple the membrane, unless you know the roofer is coming before it rains! On a related note (I am not a roofer) are you/is the roofer using counter-battens?

Where does your rainwater go?

It does but how would you detail the 'raw' PIR perimeter on the outside - just a timber (or Alu?) fillet?

Yes, FM330 is air-tight foam.

Strictly it does not help the paint adhere to the building; it (and a bit of scrubbing) takes off any algae to which the paint would otherwise adhere, rather than to the brick. If you paint over the algae - algae falls off; paint falls off. After application of the algaecide you once more have propitious conditions for the paint to stick to the wall.