With all the excitement and trauma of the spider incident (hey, I live a quiet life you know!), I was too busy staring nervously at the darting shadows from flickering candles and firelight to notice my stove flue was smouldering at the collar. I happened to notice a glowing edge where the wood met the flue and put the fire out in a right panic.
I thought there should maybe be some fire cement or something between the metal and the wood and that I hadn't been doing my maintenance properly. But when I phoned up a nearby chandlery, they said there should be a good-sized gap between wood and metal, which makes sense.
Now I'm chipping away at the charred edges which won't look pretty but will hopefully avoid a disaster.