For anyone browsing Links Beat, here is a clear starting point on the subject.
Most heat leaves an ordinary home through draughts, thin curtains and an uninsulated loft, and all three are cheap to fix. Draught strips around doors and windows, a brush on the letterbox and thick curtains closed at dusk make a noticeable difference in a weekend. Topping up loft insulation to the recommended depth pays for itself within a few winters.