There was a strange smell in my kitchen, a kind of damp smell, watery in some way. I was boiling the kettle for a cup of tea at the time, and while waiting for it to boil I first checked the washing machine (no smell), then the laundry on the floor (no smell), then the sink (no smell) and then every other conceivable place and object. Then I remembered that the scale filter had come off the inside of the kettle and I had not replaced it. Thinking this was the culprit, I picked up the kettle and smelt that. Again, I did not find the awful smell.
I have learnt two things from this: firstly, I still do not know where the smell is coming from; secondly, sniffing the steam from a boiling kettle burns the inside of your f*&%$% nose.