There may be -5 (centigrade) outside in the UK tonight.

With a gas fire inside even in an open plan house you are likely to be 16 degrees ish. Run that gas fire!

Use clingfilm and sellotape to double or treble glaze all windows.

Make sure the loft hatch shuts bubble tight (draught excluder).

Make sure the front and back doors shut likewise.

Run the immersion heater overnight every night.

Keep an eye on freecycle for rolls of loft insulation.

Keep an eye on freecycle for calor gas heaters. They produce moist heat, but quite alot of it. You will have to buy the gas cylinders but shop carefully and you will get a 12Kg one for about £15 and it will last most of the week.

Keep an eye on boot fares and similar for paraffin heaters - illegal to use in most cases these days and do NOT knock them over. The ones sold for greenhouses are cheap. The so-called "big red" produces a LOT of heat as does one of the three inch Alladins if you can find one, and a £4 gallon of paraffin will last most of the week. THESE ARE VERY DANGEROUS IF KNOCKED OVER.

How old are you? If you are a pensioner the local authority may help. If you have young children ditto.

What is wrong with the heating?