James Corden Performs as Mary Poppins for Crosswalk Musical in London

James Corden did the most British thing ever -- besides high tea with the Queen -- when he dressed up as Mary Poppins and paraded across a London street singing her greatest hits.

Corden's late night show is shooting a few episodes across the pond to air next week. He has a recurring sketch called Crosswalk the Musical where he dresses up and sings in the middle of crosswalks. He's done it before with "Beauty and the Beast."

No detail was left out for James' Mary Poppins bit ... Julie Andrews would be proud.