This morning whilst vacuming the home, I decided to push out the sofa as it has been quite a while since I have vacuumed the area behind the sofa and discovered a hole about the size of a fist in the corner of the wall in the living room. My immediate thought was that the damage was caused by a rat or a mouse, but on inspecting it closely, I saw that the wall was damp and then when I shined a light through it, I could see a pipe and it was wet and it smells a bit. I tried looking it up on what this pipe is and seems like it's an internal soil vent pipe. There would be water coming out of it when the toilet upstairs is being flushed. My guess is that this leak must have been existing for quite some time for it to do this kind of damage to cause the plaster in the wall to break apart. I have not come across this type of leak before where the sewage pipe/soil vent pipe is inside the property and boxed in using plaster wall - I thought sewage pipes would be installed externally outside the property. This looks to me like it's going to be a big costly repair job as it looks like they are going to have to knock down the wall to get access to the pipe, investigate where the leak is and then re-plaster the wall again. What a nightmare! Had I known, I would have had second thoughts about moving into this property!
