Internal insulation
The internal insulation of homes does not require planning permission. On listed buildings, listed building consent will be required.
In most properties built after the 1920s, the external walls are made of two layers with a small air gap or 'cavity' between them. If your home has unfilled cavity walls, a considerable slice of your energy bills will be spent heating the air outside. Filling the gap between the two walls of a house with an insulating material significantly decreases the amount of heat which escapes through the walls.
Solid walls lose even more heat than cavity walls; the only way to reduce this heat loss is to insulate them on the inside or the outside. Internal wall insulation, including readymade insulation/plaster board laminates or wooden battens in-filled with insulation or flexible linings, does not require planning permission.
Further guidance on internal installation can be found in the Retrofit Internal Wall Insulation - Guide to Best Practice publication on the GOV.UK website.