It's really difficult from that photo!
But, as well as a coccoon, I think you should consider it being a case-bearing larva of some sort.
Keep an eye on it. If it moves (like by tomorrow morning), it is not a coccoon, it is a case-bearing larva.
There are quite a few larvae who protect themselves by carrying around a tube with them, and hiding inside it. The tube can be built of various types of detritus (tiny stones, fragments of dead plant material, etc.)
Here's an example - Luffia ferchaultella, a moth - http://www.conwy-camera-club.org/?p=6680.
And here's a video of a bagworm moth larva, its 'bag' being composed of little sticks - https://www.youtube.com/watch?v=BKo3muYIXGE
Whereas some insects have evolved over great periods of time to accomplish camouflage through their skin (and maybe their shape) mimicing their surroundings, these case-bearing larvae actually use their surroundings directly as a means of camouflage. It is a neat trick.
So what's it doing in your house?
We'll get to that once we have a better photo, hopefully?!
BTW, it is probably harmless.
Thanks for the quick response. I don't think it is a case-bearing larvae -- which is a shame, they look quite interesting!
Yes, sorry, it was hard to photograph because it's hovering over a table and bookshelf, but I did a bit of scrambling and got a better shot.
I also gave it a very gentle nudge and can tell you it's quite firm; it looks almost like a slug, but definitely feels hard!
My house is an old Victorian ramshackle thing with all sorts of possible entry points for small guests...!
Thanks for the further photo.
As you say, it is a coccoon; well a chrysalis in one sense or another.
It shows it well enough for me to know I don't recognize it, unfortunately.
Fingers crossed somebody else will be able to help.