insulated plasterboard

What is the advantage of having a huge cavity.

I think we need to completely rethink how we construct our homes and not just try to make the way we learned how to build to fit the new regulations. In my mind they are not compatible. The only reason for the cavity was to protect from moisture ingress. This can be done other ways. Rain screen cladding with external insulation board for example.

I designed a few homes not too long ago that are near passive. They were all built block on flat with all insulation on the outside and had conc first floor. This gives maximum thermal mass/balance with any solar gain being absorbed during the day. It's is also a very cost effective method of construction.

Very important to all this is aspect air tightness and HRV.

I think a key piece of the jigsaw here also is your heating source. If you are using a geo system with underfloor where you are trying to maintain a constant temp in the house 24X7, then you have to think about thermal gain here, which was eluded to by Beyondpassive earlier in this thread, let the block work retain some of the heat. I think if you are using more conventional heating system, such as radiators, the drylining might make more sense. shorter bursts of heat that you are trying to retain inside the envelope longer. People sometimes assume today all new builds are underfloor. Some people dont like the sweaty feet syndrome and are going for Radiators (alu even)..that business is not declining as much as one might believe.