Open pipe in attic

[frasefrase]

Hi, wondering if anyone can advise on this. I live in a top floor flat and in the attic I have an open pipe that has a trickle of water running out which is starting to wreck the ceiling. I have managed to protect the ceiling by putting cardboard etc down to absorb any water, but it's getting to the stage I need to do something about it. I've no idea what the pipe is, so hopefully someone will be able to advise. I have attached a couple of pics for review. I think it could be the main waste water pipe that runs down all the flats, but why would that be open in my attic? Cheers

[stoneyboy]

frasefrase,
If is smells foul then it's probably the top of the soil system which has been forgotten. In this case get a 90 deg bend and air admittance valve and fit these.
If there is little smell it could be a vent for a bathroom or kitchen in which case it needs to be connected to outside.
See if you can trace where the pipe runs - this may give you clues as to what is connected to it.
end