The conversion will definately require B Regs which will cover means of escape from the room, ventilation to the room(s), insulation to the ground floor for sound, and new insulationto walls and floor, new heating and controls, and almost certianly some tanking to the walls, and dpm to the floor. You seem to suggest that this is not a habitable area at present. Speak to the LA building control dept as this may be far more work than you first thought. Also if you require a sunken area to accomodate the escape window as there will be a limitation on the hieght to the cill of 1100mm.
With regard to planning it will depend on whether the building is listed or in a conservation area and if you have to do any external work but I would suggest you check!!
Hope this helps.
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