“You and whose army?” What does this expression mean, how is it used and where did it originate? Is it a UK thing only?
Well, when I say it (and I’m not in the UK), it’s generally in this type of context:
Brother: I’d have kicked his ass.
Me: Yeah? You and what army?
Meaning, he couldn’t possibly do it on his own, so what army does he plan on having back him up?
Etymology I have no clue on.
Not only a UK thing, I hear it in the US.
Normally in the following exchange:
Tough Guy #1: “I’m gonna kick your ass all over this bar!”
Tough Guy #2: “Oh yeah? You and what/whose Army?”
Implying TG#1 would in no way be able to harm TG#2 without many trained reinforcements.
I always heard it as, “Oh, yeah—you and what man’s army?”
For some odd reason, I find the similarities between my post and **UncleBill’s ** astonishingly funny.
I need a nap.
There is a famous quote “How many divisions does the Pope have?” that falls into this context. I’ve seen it mostly attributed to Stalin, but also to Napolean and Frederick the Great. I suppose the idea of needing an army for support goes a long way back.
This is along the same lines as bring your lunch.
Other guy “I’m gonna kick your ass”
You, “You had better bring your lunch, it might take awhile.”
You are Crazy.
I’m pretty tall, so I had a different version.
Carey Jakes: I oughta kick your ass.
Nott: You and whose stepladder?
I always answer this with “The Army of the Potomic!”.
I’m wierd that way.
Growing up, our stock anwer to this question would be “The Girl Scouts”.
Ours was “the salvation army.”
Its a saying that implies that someone doesnt have the ‘contacts’ to go through with a plan, scheme, or act.
Either that, or, they won’t support him.
Didn’t even know it was used in the UK. To me it always sounds better in a fake Brooklyn accent.
The stock answer to “you and whose army?” when I was growing up was “me and my army, the one up my sleevey”.
I’m not big on US accents. In my head I’m hearing “Yoo and hoose oimy?”
Is that the kind of thing? 
More like “Yoo 'n hoose awmy?” I’d say.
As for Brooklyn accents, Webster’s http://www.websters-online-dictionary.org/definition/english/ac/accent.html
says that Bugs Bunny was given a Brooklyn accent.
For a more genuine one, go to http://www.transom.org/shows/2004/200402_salt.html
Find the show “Laid Off”, and listen to Tony talk.
Think Travolta in Saturday Night Fever or Deniro in Analyze This.
I found a kid in a 1952 US comic strip using it to sass his grandmother. So I got you back that far at least.
BTW, his grandmother didn’t need any help, as the last panel showed. 