We are where we are, so this is about what next and where we (well more 'him' than 'we' actually, someone I help out here in Italy in return for a kitchen) are is 300 thick hollow block walls between enormous concrete columns and ring beams to be covered by 100 XPS and then a self supporting natural stone wall 200-250. Window and door reveals will be bricks in the natural stone and I thought that the brickwork could come around the corner of the wall insulation just enough so that the Window frame’s inner edge (say 10mm) is adjacent to/overlaps the internal block-work. The front face of the frame pushes up flat against the brickwork with the tape See link below) from Wookey's Window post making a good seal, as per pics 1, 3 and 8 in the link. The frames are stuck in with expanding foam; frame-fixings could used as well, though would be going into insulation unless put in at an angle (only possible if the screws heads didn't then interfere with the window closing). The window’s position ensures the external brickwork is kept as far away as possible from the internal walls and as the XPS/expanding foam, window and seal tape are all impermeable the water is kept out. Internal finishing is then coarse plaster over a type of spray on internal render that they use over here up to expanding foam and the window frame (plaster could also be sealed to internal face of window frame with thin bead of caulking).

Or his idea is to use cavity closures from UK (you can't buy them here) and DPCs throughout and I've never even seen one so my question is do we need them? Or, put another way, how best to fit the windows (?) because the local way is to take these Argon filled 2G windows and attach them to a metal frame that extends across the whole width of the wall, being embedded into both the internal and external walls. In their defense, when I mentioned cold bridges they (window manufacturer and installer) suggested we use wood frames.....

Here's the link from the other thread (BTW thanks):
http://www.customaudiodesigns.co.uk/acoustic-expanding-foam-tape.htm

Supplementary Q: we were not planning on a membrane between the XPS and the insulation, comments?

Forget building control, we are pushing their envelope with insulation across the concrete columns and beams - they are so thick we don't need it I was told, decrement delay perhaps! The house will have adequate 'always on' ventilation.