I always put my fiance down as next of kin even though I have living relatives including two adult daughters.I do this mainly so if I am ever involved in an accident they are not informed first and can have the news broken to them by a familiar person.I think for things like medical forms you can nominate anyone you like as next of kin.You can also put no name in if you want.
Thanks daffy, I recently attended hospital following a heart attack and the staff required a next of kin, when I said there was no-one it caused great confusion, they eventually settled on my GP. I'm sure this situation must arise quite often and wondered what happens in other hospitals.