Pipe leaking from cistern to bowl, pipe thick black sort of scaly growth?

The pipe has obviously been leaking for some time. Has thick black 'growth' on the pipe, the leak has dripped down on to back of toilet and onto carpet. Smells more like a public loo when you open the door! Yuk! Room is tiny, hardly any room to move, and having spinal probs can't bend very much or for very long. Get black marks on bottom of toilet (under water line), but when you look really closely, it appears as if there's something 'moving about in the water', reminds me of something you would see under water on a nature prog. When cleaning bowl with brush, if clean under rim often get big black chunks of ?limescale dropping down. The property was built c. 1968, it is a pink suite, Royal Doulton Vitreous China is printed on the bowl. Really need to get this cleaned up urgently, pipe and 'growth' look horrendous. Wondered exactly what this was, what would easily clean it up, and without too many fumes. Desparate for any help!!