In reply to BedRock:
I've lived in about 4 different flats (in Edinburgh) which all had single glazing. However, there were huge variations in how easy they were to keep warm. The main issue I've come across is not necessarily the single glazing, but the old wooden window frames/sills. In some of the older properties there were quite sizable gaps between the window and sill, making it really draughty. However, this will be difficult to identify without viewing the place.
Our flats would generally cool down to about 12-15 degrees overnight (it being heated up to 18-20 degrees the night before), but once got down to about 9 degrees after we came back from a week's holiday in winter. I've only lived in flats though, so an end-terrace house might be very different.