Shimrod said "Curiously, although I seem to be able to hold a tune on my own, I find it difficult to sing in tune with other people (I'm pretty convinced that I invariably sing flat in choruses); I just can't seem to relate what the others are doing to what I'm trying to do - does anyone else have this problem?"

I'm absolutely convinced I get the same thing (the bit about chorus singing anyway - not so sure about the bit about holding the tune on my own!). I get the same problem if I try to sing along to a record or an instrument.