Hi. I was reminded on an old Jackanory episode the other day, but I can't find anything about it on the internet, so I thought I'd try here!
It must have been about 1971, and scared the bejesus out of me, as I was very young. The story concerned some children who hear a noise in their loft, and see a strange creature called a Dervish sitting there. I remember from the illustrations that it looked a bit like a giant head, with arms and legs. Somehow the children end up in the dervish's land, where people are killed and used as slaves. I seem to remember the only way to kill them was to throw something in their huge eyes (salt?).
I would be grateful if anyone remembers this, as I would like to try and get the book!