When is it acceptable to escalate defects beyond the developer?

[MidsNewBuild19]

Short version of the story, we moved in to our new build in 2018 and since then we have had a number of defects/snags which have been, or are planned to be fixed.

However a couple of issues in particular are really troubling me, specifically relating to coldness in the property.
I found out the insulation in our 3rd floor roof space is not to drawing, other issues include:
Extractor fans not connected to the roof vent
Downstairs toilet extractor not connect to external duct
Gaps in window and door sealants.
A recent thermal survey also found some internal cold spots along ceiling edges.

I believe the combination of these issues will be contributing to the increased heat loss from the property, particularly the unconnected vent from the downstairs toilet which is effectively an open 4” duct feeding the space beneath the 1st floor. I can literally see the floor joint when I look from outside.

The developer is on the last chance to resolve the insulation issues and the NHBC are awaiting my evidence should they fail to fix this. With the additional issues noted more recently, and given they are non-compliant to building regulations, does it seem fair to escalate this further?
Either for compensation due to increased energy costs, or for independent inspections from the local authority?

[New Home Expert]

I would agree that as you are still having unresolved issues since 2018, you are due some compensation settlement.
I think you have been very patient for what is a very poor quality home.
All extractors should be connected to the outside air. You will have mould in the roof space by now.

I suggest you make a small claims court claim for your quantifiable losses Extra energy costs and an amount for the effort you have put in and inconvenience.