I've always called mine Mummy and Daddy, although I'd never say 'Mummy can you pass me the ketchup' cos I do feel a bit strange still using Mummy/Daddy so I avoid it as much as I can. However, if I was speaking to my dad I'd say 'Mummy wants you to get some milk'.
I do feel a bit embarrassed that I call them Mummy and Daddy and I'd never say it around my friends, but it would feel really odd all of a sudden saying Mum/Dad. I think one of the reasons I feel a bit embarrassed is because of the sexual connotations of 'Daddy'. I'm not sure what I'll do when I'm in my 40s, I might just call them Mother/Father. Calling your parents Mummy and Daddy is quite common for posh people though.