Today’s Regency-era research topic was regarding what might be implied if a gentleman offered his arm to his friend while they were out walking. I found my way to The Laws of Etiquette, by A Gentleman, which is American, but makes great example of the manners of Beau Brummel and generally observes English etiquette.
My favorite excerpt from this delightful little treatise was “If you accompany your wife to a ball, be very careful not to dance with her.” Oh, the very idea! Such scandal!
The gentleman author did somewhat answer my question thus:
If you are walking down the street with another person on your arm, and stop to say something to one of your friends, do not commit the too common and most awkward error of introducing such persons to one another. Never introduce morning visitors, who happen to meet in your parlour without being acquainted. If _you_ should be so introduced, remember that the acquaintance afterwards goes for nothing: you have not the slightest right to expect that the other should ever speak to you.
The gender-neutral usage here seems to imply that it would not be unusual for friends of any gender to link arms as they walk down the street. I’ve seen plenty of Regency-era paintings and drawings with two ladies walking with linked arms, and it seems to me that it would be in no way unusual for two gentleman to walk with linked arms, just as it was perfectly normal and acceptable that gentlemen should dance with other gentlemen at a party if there were insufficient ladies. (A social custom which I put to frequent use in my stories.)
I am continuing to seek clearer evidence on all these topics.