Its important to know if you have Cavity Walls or Solid Walls before considering what type of wall insulation you will need, most properties built after the 1930's have cavity walls which is two separate walls with a cavity (space) in between them. Although the original purpose of the cavity was to prevent damp moving from the out wall to the inner wall, it was quickly realised that this cavity could also be used to help insulate the wall by adding insulation between the two brick layers and over the years the cavity has gotten wider and wider in order to accommodate additional insulation.

This is how you might check your home to see if you have cavity walls or solid brick walls:-

https://youtu.be/kkOC1hvyfuk