I could tell that Mitzi needed a poo this morning, just by looking at her tail so every hour after we came home I opened the back door in case she wanted to go out but the closest she got to the back door was half way into the kitchen.
Steve went out into the kitchen to make us a couple of hot drinks and discovered that Mitz had poo'd in the middle of the floor.
It wasn't there when I came back into the living room and she didn't ask to go out, so there was literally a 5 minute gap she could have done it in.
We'll know better for next time though... I'll open the back door and leave it open so that she can take herself out and has the privacy she craves.