I noticed the vile little creatures as I was coming down the stairs. There were a dozen of them on the plastic threshold just inside the front door. I scraped them up and dumped them in the garden. They were about 10mm to 30mm long and alive (wriggling). Quite disgusting, since I am squeamish about such things.
So what could I do to prevent them in future? I assume they're attracted to the warmth of the house.
MM