In most other parts of the world all medical practitioners, physicians and surgeons alike, are referred to as Dr while in the UK surgeons are usually referred to as Mr/Miss/Ms/Mrs. This is because, from the Middle Ages physicians had to embark on formal university training to gain possession of a degree in medicine before they could enter practice. The possession of this degree, a doctorate, entitled them to the title of ‘Doctor of Medicine’ or Doctor.
The training of surgeons until the mid-19th century was different. They did not have to go to university to gain a degree; instead they usually served as an apprentice to a surgeon. Afterwards they took an examination. In London, after 1745, this was conducted by the Surgeons' Company and after 1800 by The Royal College of Surgeons. If successful they were awarded a diploma, not a degree, therefore they were unable to call themselves 'Doctor', and stayed instead with the title 'Mr'.