Telesales are an enormous irritant and I would not want to say or do anything to suggest it has any merit apart from providing work for a few desperate souls. However,...
In relation to the climate, an inordinately high percentage of the UK housing stock is substandard. Considering the comfort levels many western nations now expect, the same UK dwellings are barely fit for living in. This is because it is increasingly common for people to, while indoors, expect to be able to be independent of outdoor conditions without too much financial effort in terms of running costs. This is not the case if when it is cold outside it is inevitably also cold inside. The ubiquitous old slide-up-and-down windows, apart from single glazing, are so draughty that it is impractical to try to heat the place much past 10 degrees when it is below 5 degrees outside and windy. It is possibly a uniquely British solution to try to draught proof and insulate a dwelling with heavy curtains - but, admittedly one that has some effect in a near hopelessly British situation. Such draughty windows are still widely found in the UK and they are still in houses on all sides of mine.
The time it takes to recover the cost of replacement windows is usually measured in the time over which the savings in heating costs equals the cost of the windows. I installed central heating in our house in 1973 and completed replacement with double glazed windows everywhere within eighteen months of that. I would not be surprised if the pure cost analysis by the above criteria were to result in recovery in about five years but in terms of simple comfort the cost was worth it from the moment of completion of installation. My assessment is based on the fact that we heat to a constant 21 degrees while we are awake and a minimum of 18 degrees at all other times. We simply would not be able to maintain those levels during cold/windy weather with the original windows in place - unless we had a far more powerful heating system approaching furnace output in every room.
The time it takes to recover the cost of replacement windows where heating is solely used to maintain no more than 10-12 degrees minimum in some rooms and at best 18 degrees temporarily for part of the day in a room or or two will be far longer because of the small temperature margin they are working to. In houses where there is scarcely any use of heating, clearly having windows to post 1870 standards or so is a waste.