I have applied a foam wallpaper (10mm thick) to the insides of all external walls in my Victorian house -it has made a big difference to the insulation. Not cheap but worth it. It is manufactured by Sempatap.
Outstanding custom made, double glazed window sashes from QuickSlide in Yorkshire; excellent value for money -highly recommended. Superb quality!
Solar PV has been the best investment we've made even with low levels of daylight this year. We combine it with the Economy 7 tariff so we run appliances, immersion heater overnight at the cheap rate -a huge saving. Electricity prices are set to rise considerably too over the next few years so these things are really worth doing. I can't understand why Economy 7 is not being promoted nationally as masses of power is wasted overnight.
I plan to instal a voltage stabiliser (VPhase) to ensure all incoming power is at 220 volts and not more.This should save 10% of electricity consumption.