Caporegime
@Minstadave Could it be you have a leak in the chimney breast and what is coming down is old soot from when the chimney was used with an open fire?
I dont think so. Its a 90s build and don't think it's ever had anything other than a woodburner.
Our chimney sweep says it's solid (clay?) lined chimney and it must just be a small leak where tar is trickling down and should be directed into the woodburners flue pipe but isn't.
I'm reluctant to spend 2k lining the chimney if it doesn't need it. I'll see if I can get someone to scope it to see what's what before ripping it all out.