You should also consider:
Loft and Cavity Wall Insulation – Undoubtedly cavity wall and loft insulation will greatly reduce the amount of heat lost but equally significant is the amount of heat lost or wasted through old inefficient windows and doors.
Windows and Doors – Install or upgrade to Elwyns energy efficient double glazed windows and doors.
A New Boiler – If your old boiler is more than 10 years old then you should definitely consider having a new boiler installed. There are now more energy efficient boilers available that could save you hundreds of pounds per year. Get your old boiler checked now.