Everybody has been sharing this video today - and once you watch it, you'll know why. It shows London circa 1927 through the eyes of one Claude Friese-Greene. As the description that came with the video explains, this is "incredible colour footage of 1920s London shot by an early British pioneer of film named Claude Frisse-Greene, who made a series of travelogues using the colour process his father William - a noted cinematographer - was experimenting with. It's like a beautifully dusty old postcard you'd find in a junk store, but moving." Indeed.
I'm pretty sure this is part of a 2006 BBC documentary - co-produced with the British Film Institute - called The Lost World of Friese-Greene. Originally this clip was pat of his project called The Open Road whose aim was to film the people of Britain in colour for the first time.