If your property has solid walls, rather than cavity walls, you can work to insulate them from the inside or the outside.
Common in homes built before 1920, properties with solid walls let through twice as much heat as their cavity wall counterparts. While they're more expensive to insulate, savings are greater in the long term; it's estimated that homeowners could save up to £490 on their heating bills each year.
Internal wall insulation involves fitting rigid insulation boards to the wall, or by building a stud wall filled with mineral wool fibre. Stud wall insulation is thicker than rigid insulation boards, reducing the size of your room.
A stud wall is strong enough to hold heavy fittings such as kitchen units, radiators and washbasins, while insulation boards (typically between 60-100mm thick) need fixings that go through them and into the original wall behind.
Externally you can attach a layer of insulation material to the outer wall, and either clad or plaster over it, depending on your preference.
Generally cheaper to install, internal wall insulation is more disruptive, in terms of building works throughout your home and the need to remove internal fittings, skirting boards and doorframes in each room.