There are a few things going on here, my comments are in no particular order:
1. The pebble dash is likely to be a cement based render, not breathable, and thus is trapping moisture within the wall which would otherwise escape to the outside (if you had a breathable lime based render externally).
The pebble dash on your house is almost certainly not original. Your walls would originally have been limewashed externally, so I am not sure why the Local Authority would have a problem with you reverting to a lime render on the external face if this was pointed out to them. You should look into this in any case.
Lime rendering should only be carried out by a specialist.
2. You have a problem with a lack of ventilation in the house, thus a lot of moisture is trapped in the air. This will condense on cold surfaces.
3. You have a problem with insulation, which results in the internal surfaces being cold, and thus inviting condensation.
4. You need to be aware of, and treat, the ventilation and insulation problems hand in hand to insure a healthy living environment. This is very important.
5. Drylining, if carried out correctly and carefully (i.e. fully sealed from the stone walls with a membrane) will work, but if it is done incorrectly it will lead to moisture build up on the inner face of the stone walls, which you won't see, won't be able to clean, and will lead to mould. This will cause problems with degradation of the building fabric, and may well aso have health implications.
Many builders do not seem to be aware of this fact.
6. In regard to the roof, you will need to ensure that when you insulate it you leave sufficient space for ventilation between the roofing felt above and the insulation below. You are very likely to need slate vents in the roof to ensure airflow over the insulation (thus pulling off any moisture which will build up in this area).
You should also double check if your roof is leaking or not.
I would suggest that in the first instance you contact an Architect or Architectural Technologist who has experience with old buildings of this type and ask them to carry out an inspection.
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