Most properties built prior to 1930 were constructed with solid walls, so they don't have cavities that can be injected with insulation. These solid wall properties can be insulated with external solid wall insulation.
External wall insulation is a great way to protect against penetrating damp, creating a new weatherproof layer on the outside of the building, and slowing the movement of heat through the walls. Another advantage of solid wall insulation is that it will cause the temperature of the walls themselves to rise. This means if there is lots of water vapour in the air (from cooking or washing for example), this will no longer condense on these walls.