The fact is, the Robust Details have not been complied with and your property has been falsely certified as being constructed to the specific requirements of the detail.
It does not matter if the specification you were shown at reservation for the type was different as whateverit is, it must meet the requirements of the building regulations, by law!
The NHBC are most likely to have been used by Barratt for building control as well and warranty inspections. It is much better if the actual Local Authority undertake building regulation compliance inspections.
Note this is NOT the same as LABC warranty building control inspections.
It is clear that the insulation under the floor is missing. From what you have aid it is also highly likely that the perimeter isolation of the floor above has not been installed or badly executed.
Quiet how this could be judged as meeting and complying with Part E Building Regulations I don't know.
Perhaps you should write top Barratt CEO Dave Thomas Email is
david.thomas@barrattplc.co.uk and ask him why his supposed 5 star rated company is fobbing you off?
You can also complain about building control non-compliance with your local authority who have powers to enforce compliance remedial works. Failing that, you can complain about this to
http://cic.org.uk/services/complaints.php