Actually, AIUI it’s rhyming slang, from china plate → mate.
I wouldn’t go a week without saying it, mostly to locals as we pass in the street sidewalk footpath.
This from the nation that stuffed an utterly superfluous e into whisky?
If extra letters are a bother, drink rum.
Khyber = Khyber Pass = Ass—I assume that’s American because of the rhyme, but I don’t know. I haven’t encountered it in the wild since I was a kid last century.
“Tea” as a regionalism for “supper” confused me at first (“what are you having for tea?”)
Americans have been having this issue for two or three decades wherein “literally” has become a contranym, meaning both “literally” and “figuratively”. I get the impression that this has not really infected British English. Do I get the wrong impression?
Actually Pass rhymes perfectly with Arse in BritEnglsh.
Explanations of rhyming slang remind me of when Niles Crane, cast into a singles apartment, related how his name at the complex went from Niles to Coyote.
That’s not an American saying. I have never heard or read that once in my life.
Whiskey with an E for men who are free
I’ve heard the “Khyber” reference before, but only in the context of the film, “Carry On Up the Khyber.”
It was one of those British “Carry On” films, this one set in British India during Victorian times. I saw it as the B-picture at a drive-in double-feature. My parents chuckled knowingly at the title; eight-year-old me didn’t know why, but the film was a funny comedy and I enjoyed it. Of course, now I know what amused my parents.
I wonder if that’s where “Sweet Fancy Moses” originated. 
One I like is ’ earwigging" for eavesdropping.
I have, as both “aitch” and “haitch”.
The figurative use of “literally” can be traced back to British writing 300 years ago. It is not, in any way, a new corruption.
Whether or not you’re more or less likely to hear a current British speaker say it compared to an American, I don’t know, but in a historical sense, this usage has been around literally forever.
Oh it absolutely is used a lot, and it literally boils my piss (not really… but it is annoying).
British military - “pass” and “arse” rhyme in BrE, and the Khyber Pass/North West Frontier of India was a notoriously unpleasant posting.
This is correct. The term ‘river’ can apply to quite small bodies of flowing water, because the naming is historical rather than some technical specification.
Creeks are tidal inlets that may resemble a river, but typically have no significant fresh water flow.
English English - it doesn’t rhyme in Scottish English.
This is true of slang in general. How do you divine the meaning of terms like rizz or GOAT or yeet, without just learning what they mean?
When it comes to slang, I’m reminded of the language we use at the horse race track. Rarely profane, but if you don’t know what we’re talking about, you’d understand it as English, but not understandable English to anybody not in the know.
Somewhat similarly, I spent two weeks with friends in Coventry, UK once. Of course, I met their friends, and at first, was puzzled by their greetings. “Hello, Spoons, are you all right?” It took me a while to understand that what they were saying was the equivalent of, “Hello, Spoons, how are you doing,” here in Canada.
To be fair it probably doesn’t rhyme anywhere north of Watford Gap.
I remember when I was in high school, and our family was eating dinner. No idea how it came up, but I said, “At school today, So-and-so said, ‘XYZ’ about Bla-de-bla. Well I could tell that he knew SFA about Bla-de-bla.” I, of course, meant “Sweet Fuck All,” which in those words, would have been inappropriate in front of Mom.
Innocently, Mom asked, “What does ‘SFA’ mean?”
Dad, knowing exactly what I meant, saved me the embarrassment. “It means, ‘Sweet Fanny Adams,’ or in other words, nothing.”