Navigating UK Culture and Etiquette

I have several friends whose careers has taken them abroad and as a result they are now residents of other countries. Two live in the US and one lives in Australia. Whenever we catch up socially they quickly fall back into what I describe as “British Mode”, despite the occasional lapse into a US or Australian accent or the use of a word or phrase specific to those countries. All of them are fully integrated into their respective new homes and societies but at heart they still remain a Brit. There are some very particular cultural foibles and matters of etiquette that make for this very specific distinction. I have noticed them myself when speaking with my US colleagues online. I spent several years co-hosting a podcast with my American friend Brian and every now and then, they’d be a pregnant pause in our discussions because one of us had referenced something unknown to the other, or touched upon a social difference that discombobulated the other.