It's turning out to be very difficult to keep up the air-tightness, now that we've got various other trades involved. As well as the Proclima air-tightness tapes that you've seen in previous posts, sealing of cracks and around pipes etc is done with Orcon F (not sure what the F stands for), a green-coloured sealant that's applied using the same type of gun+nozzle as you would apply eg bathroom sealants.
Unfortunately, the limited number of places that actually sell Orcon F are closed between Christmas and New Year, so consequently a few jobs have had to be "paused" until 2 Jan, when my delivery of the stuff is due. I look forward to the day when it can be picked up from Screwfix!
Here's an example of the challenge: a bathroom waste pipe, which has to penetrate the front wall insulation to reach the outside. I thought the penetration had been adequately sealed but when, for a completely unrelated reason, we removed a section of the floor in the bathroom, it turns out the hole the plumber had made for the pipe remains open within the floorboard depth. Obviously, I took the opportunity to make good (this was before we'd run out of Orcon!).
Unfortunately, plumbers, kitchen-fitters, etc can very easily come along with power tools that can decimate your air-tightness performance in seconds - and be completely oblivious to this. There doesn't appear to be an easy answer to this problem, other than standing over them constantly!