Great thread: very helpful.
We are going to do the clingfilm glazing thing while we faff about prevaricate about replacing windows.
Few other tips not already mentioned.
You can also buy thermal blackout lining by the metre either from John Lewis or ebay - not very expensive. You can then staple, pin or velcro over windows in winter.
Re line curtains with a layer of this too.
If you have concrete, brick, stone floors under your flooring, consider putting extra layers down, either with rugs, extra underlay or extra/better stuff under a floating floor - for example if you've a click together floor (engineered wood or laminate for example) make sure it has a damp membrane and the best quality insulation board too.
This makes a big difference in houses with solid floors and imagine will make a smaller difference with suspended floors.
Stick draught excluder round every door and window and use thick curtains over doors.
Sounds simple but CLOSE doors between rooms when heating them and try not to unecessarily open and leave open - especially applies to outdoor doors.