I live in a flat in London. Today I changed a downlighter bulb and about 30 of these fell out as I removed the fitting from the ceiling. They are all dead, I presume cooked by the heat of the light. They were existing in the ceiling space between ground floor and upstairs. Any ideas? Should I be worried?
Probably belongs to the Dermestidae family of beetles. If I had to guess (which I do, so I could be wrong!), they're carpet beetles of some sort; though not varied carpet beetles, which have a distinctive patterning. The larvae like to feed on organic material such as carpets and other textiles, but also old birds nests, dead rodents, etc. The larvae are known as woolly bears, e.g. see the images in this old thread:
If I'm right, it's possible that you may have a pest problem should you start finding lots more of them, in which case you'll need to contact your council, or it could be that there's a single food source (perhaps a dead rodent?) between the two floors.