I used to work in a central London vets.
We have a working cocker but have sullied our middle classness by also owning a staffie
A staffie is absolutely permissable in a UC/MC household provided it came from Battersea or The Dogs Trust. You must of course inform everyone of this.
The solidly MC and UC clients generally had gundogs (labs or spaniels - usually with names like "Grouse"), whippets or other working breeds (a few Dalmatians, Newfies, Wolfhounds and an absolutely glorious Leonberger). If they had graduated to full pack status, throw in a few terriers and some odd-looking Greek rescues that may or may not have been dogs 
The blue shar pei - not posh, although very handsome!
Blue was nouveau rich circa 2010-ish.
Today its dilute, lavenders, & idiots breeding double-dapple dachshunds with all the health problems they risk, sadly.
See also frenchies, pugs, doodles etc (I did meet one v posh frenchie but he was ancient a decade ago so bred prior to their rise in popularity!).