Though confusing to some, in the past, particularly in the UK, there was a strong distinction between physicians and surgeons. Physicians were usually considered gentlemen, and therefore treated with the courtesy of one, being allowed to enter through the nobility’s front doors and such. It was believed that surgeons, on the other hand, were of a lower class because they performed manual labor, something a gentleman did not do. So while a physician could examine you and prescribe medicines, a surgeon had to be called in to do bloodletting or set a broken bone or perform any type of surgery. Surgeons were consequently treated like the lower classes, entering through the servants’ door and being denied entry to the formal receiving rooms of the house. Which is why Sir Anthony would never have been permitted even to court Kiera had he not received his baronetcy.
Also perplexing to many Americans is the fact that most surgeons in the UK go by the title Mr. even to this day. This tradition originated in the sixteenth century when surgeons were barber-surgeons and did not have a medical degree like physicians who attended university. When the College of Surgeons received its royal charter, the Royal College of Physicians forced the law to stipulate that surgeon candidates receive a medical degree first. So an aspiring surgeon was made to study medicine first, achieving the title Doctor. Then when he obtained his diploma to become a Fellow of the Royal College of Surgeons, he reverted to Mister as a sort of snubbing to the Royal College of Physicians. To avoid confusion, I opted not to title the characters who are Fellows of the Royal College of Surgeons as Mr., but left them with the distinction Dr.
Through the course of history, there was indeed a set of special privileges reserved for the British peerage, namely the right to a trial by their peers in the House of Lords, access to the sovereign, and freedom from arrest. In the case of the latter, peers were supposed to be free from arrest in civil cases only, not criminal, but the law enforcement officials of the time, particularly before formal police forces were established, would have found it difficult to arrest a peer at any time without getting other peers or magistrates involved. Without definitive proof, Constable Paxton would have had trouble convincing a magistrate to arrest Lord Dalmay, because of his title. And even if he had been arrested and charged, Lord Dalmay would still have been tried in the House of Lords, if, under the circumstances, it ever came to that.