Cheerio! Spit-spot! Mary Poppins is set in London, England—capital of the British Empire and home to any number of cockney street sweepers and magical nannies.
But Poppins isn't set in then-modern day London (in the swingin' 1960s). It's set in the Edwardian Era, specifically in 1910, back when King Edward VII was doing his thing.
George spells out exactly what time it is, and how it feels to be a man in the era:
GEORGE: It's grand to be an Englishman in 1910! King Edward's on the throne, it's the age of men! I'm the lord of my castle, the sovereign, the liege!
George is acting like it's a man's world and he's ruling the roost—but, in reality, he's not incredibly happy as a junior member of the bank, and his world is changing around him. For one thing, his wife's become an ardent suffragette:
WINIFRED: We're clearly soldiers in petticoats, and dauntless crusaders for women's a-votes! Though we adore men individually, we agree that as a group they're rather stupid.
The campaign for gaining women the right to vote was huge at the time. Winifred mentions one of the other suffragettes chaining herself to the Prime Minister's carriage—things got intense. Eventually, in 1918, women finally would gain the right to vote in England—towards the end of World War I.
So, despite George's claim that he's the ruler of his household, he's actually an uncertain man in an uncertain world.
We also see different London locations in the movie. The pigeon lady feeds birds outside St. Paul's Cathedral—a classic London landmark—and we get aerial views of the city, including the Parliament Building and Big Ben. Plus, when Mary, Bert, and the kids leap into the chalk drawing, they enter a cartoon world based on the English countryside, except with talking farm animals and penguins who act as waiters. They do classically English things there, like participate in a foxhunt (while saving the fox) and racing horses.
Also, the London setting shapes the characters: Bert speaks with a cockney accent and George is an uptight gentleman who loves tradition and discipline while approving of foxhunts—a spot-on stereotype of an upper-middle-class conservative British guy.
Yeah. The only thing that would make this American-made movie more British is if Jane's middle name was "Shakespeare" and Michael wanted to grow up and become a beef-eater.