I've had the heating clicking on just for a short time in the morning and a little bit in late afternoon, which so far is enough. The house sits around 18°C during the day without the heating being on. We've got a wood burner to compliment the gas CH, which we use for heat and not aesthetics. I didn't use it so much in the past when buying kiln dried logs because it actually works out more expensive than the central heating, but now I put my chainsaw to work and season the logs myself, so it costs a little bit of my time and a drop of petrol/oil.
The house is crazy insulated at the attic/roof level due to the conversion, but on ground level I deliberately left the exposed floorboards with the gaps unsealed to allow airflow from a large crawl space beneath. This can cause a slight draft on very cold windy days.