LOL - I can remember that too. A paraffin heater in the hall, and if we had some coal there might be enough hot water for bath night on Fridays from the back boiler.if you're lucky. Later on we had a gas copper in the scullery for doing the washing, and I used to take a bucket of boiling water upstairs to the frozen bathroon. (No thermal mixers in those days!) The wallpaper in my bedroom used to peel off at the top every winter and hang down, then every spring we would stick it back again. Do you remember the big freeze of 62/63?
The point is, if it's cold enough to freeze condensation on the windows then the water pipes are in danger of freezing too and I wouldn't feel confident about the pipes in the loft if I left the house for a week with the stat at just 5°C. Pipe and tank insulation doesn't protect static water from freezing - it just slows down the rate of cooling.
Peter