Houses built after 1920 will genarally have a cavity wall construction, wherein insulating material is injected to greatly reduce heat-loss through external walls. Though cavity wall insulation can be expensive, the cost can sometimes be met by a government grant if you (or anyone in your home) are in receipt of a qualifying benefit.
Loft insulation is a no-brainer when it comes to reducing heat loss from your home, as over 25% of all home heat is lost through the roof because of poor or no insulation. As with cavity wall insulation, the cost of loft insulation can sometimes be met by a government grant if you (or anyone in your home) are in receipt of a qualifying benefit.