Not correct, I'm afriaid, Count.
Whether it is habitable space (or not) only becomes an issue if one is removing the original door between the garage and the rest of the house - otherwise from a Building Control viewpoint, its just a luxury garage, and a non-habitable space. As such it doesn't have to meet thermal or any other of the statutory building regs.
And it won't be a Planning issue either - unless (and this is very unlikely) the planners have an issue with the removal of an off-road car-parking space (by the removal of the space previously available to put a car).