BT80 in the loft space...If you can safely, try and get a good look inside it with a good light source. What your looking for is any hint of a greeny turquiose deposit. Its not common in an attic but I had found occasionaly it crops up. Some loft situations seem to cause a bit of humidity in cetain spots. If it does crop up then it tends to affect that line in the area on its own.
Although it goes without saying, in loft spaces be carefull, take your time an concentrate on putting your weight on solid woodwork. I was always paranoid about sticking a limb through someones ceiling, or at least bowing one. The other thing to look out for is nails or staples not completely in the wood. Really nasty to kneal on.