I noticed the paving slab at the base of the soil pipe had dropped down. Then a corner of it broke off. I had a look in the dark gap and can see that there is a gap of about a centimetre between the bottom of the cast iron soil pipe and what I presume is the drain (I can’t really see that). I can’t see that any seal has broken. The house is about 100 years old so I don’t know if it was built like that, or if a seal has gone or if there has been subsidence and the ground has moved. I did a test flush and most of the water went straight down into the drain but some splashed out. I usually get the single woman surcharge when I call tradesmen out and so I want to try to understand what this might be and how serious and what kind of plumber/drains specialist/builder I might need first. Any thoughts appreciated.