Tilly:
It's actually quite a long time since I had much 'fur' on top!
The cats do help to keep me warm, especially when Biscuit snuggles up under the duvet with me (or, as he sees it, when he graciously allows me to join him under his duvet, where he spends much of his time anyway!)
I have just given in to temptation though, and turned the heating up a bit. The new cat, who moved in a week ago, seemed to be expecting me to do so!
My last electricity bill showed that I was £430 in credit, so I can probably afford a little bit of heating now and then anyway ;-)