The question is about what can be done immediately. Insulating existing buildings is a long term project; in fact it is something that the UK has been failing

The question is about what can be done immediately. Insulating existing buildings is a long term project; in fact it is something that the UK has been failing to do over the last several decades. But reducing average household temperatures can be done overnight and in fact we have done it in the UK before in the energy crises of the 1970's when people were urged to turn the heating down to 68°F (20°C) and commercial operations were reduced to three days of operation per week.