Sherlock Holmes and the Law

I'm a big Holmes fan and recently discovered a terrific podcast about the Jeremy Brett series that remains my favorite adaptation of the stories. So I thought I'd do some fun posts about legal points that arise in the stories. For example, Holmes often gives his opinions about what juries might do in certain situations, along with other commentary.

Here's one that's not from Holmes. In "The Norwood Builder," Holmes is consulted by a client who is (falsely) accused of murder. Inspector Lestrade arrives to arrest the suspect. Holmes asks Lestrade if the client can tell his version of events before being taken away. Lestrade says fine, but then says: "I am bound to warn him that anything he may say will appear in evidence against him."

That sounds a lot like a Miranda warning, but the story was published in 1903. In what sense was Lestrade "bound" to give this warning? Does that mean "legally obliged" or "morally obliged?" Perhaps someone who studies English criminal law history would know.