First of all the NHBC warranty covers all parts of the home for 10 years. During the first 2 years it is the housebuilders responsibility to fix defects and poor quality workmanship. If they do not do so, and if the defects are as a result of warranty standards not being followed, the NHBC will instruct the builder to carry out the works. If they fail to do so the NHBC will appoint their own contractor to do the works.
As far as internal walls are concerned, the only walls within a home - timber or metal stud walls - that need insulation are those to bathrooms, WC's and SVP boxing, this is sound insulation.
All walls to the outside need insulation and any walls that adjoin another property (party walls) must have fire proof and smoke proof construction.
If Hyde are a Housing Association, I suspect the HA will say contact to builder and the builder say any complaint must come from the HA. My advice is WRITE to Hyde and demand they investigate and rectify. Perhaps then, they will force the builder to act.