Just phoned my husband, who's a doctor (consultant), and calls himself one. As do his colleagues. Surgeons call themselves Mr. According to my husband, this is because they were originally barbers, not medical people. Gynecologists apparently are starting to call themselves Mr. (or Ms.?) and some dentists are starting to call themselves Dr.
Consultants are senior (specialist) doctors, and registrars are trainees.
There seem to be millions of grades of nurses. My husband was actually in the hospital himself last summer, and I remember seeing posters showing the various grades of nurse, all distinguished by different combinations of uniform and belt color.
Interestingly (perhaps), my husband got his PhD before getting his medical degree, but never really used the title at that point.