I suspect that everything in my life eventually comes to a bad end. I had another go at the 'heat your room with 4 tea lights and a plant pot' method earlier. This time - I used a slightly bigger plant pot and 5 tea lights. It seemed to be working, more heat radiated and the plant pot pleasingly hot. I was in the kitchen for a while and could detect the odd chemical smell of candlewax - which i didn't really pay much attention to - then opened the living room door to find it full of smoke - the heat seems to have ignited all the wax and created a delightful ball of flame. The dogs were just sitting there - mesmerised in a smoke filled room. I put it out with the 'wet tea towel over a chip pan' manoeuvre and took the smoking mess outside. On the positive side - I now know I need a new smoke detector - additionally - I suppose the front room is much warmer and the smell of burnt wax isn't 'that' bad, now that the smoke has faded.
I'll pick up a new smoke detector in the morning - the one I have is wired to the mains and shouldn't have failed.