Talk to the planning office first. The plans probably state parking, not living because the building regulation requirements for a garage are entirely different to those for living accomodation. Fire regulations and Insulation regulations are required to name only two. The ceiling of the garage will have to be upgraded and the insulation of the walls (and possibly floor) will need to be shown to stay within regulation guidelines for heat retention in the room/building. The project on garage conversions may help a little but you will get most help from the planning office initially. There may be a requirement for planning permission to alter the use of the room and there will certainly be a requirement for building regulation approval. The only people who will be able to tell you if plans will (or may be) approved are your local council. Anyone else is just guessing.