Two views of Downing Street, 1926 and 2007.
It's part of the amazing work being done by the Flickr group 'Wonderful London', who seek to recreate all the panels from the book of the same name by St John Adcock (1926/7). This particular pairing was made by group admin Simon Rigglesworth, who thanks a 'PC Luton' for providing access.
Prime-ministers come and go (eventually), yet the little street rarely changes. Thanks to the protection of English Heritage, many features remain the same (EH are also responsible for the gates that bar entry to the street, installed in 1989). Even the olden-day grime has been kept. As Simon points out, the buildings would be yellow brick, but for a coat of paint to simulate a smoggy patina.
That's not to say there haven't been alterations - count the number of windows. The two right-most bays were added in 1960-4 by Raymond Erith (who also designed Jack Straw's Castle near Hampstead Heath). The building with the pyramid roof (No.12) is also from the 1960s, by the same architect.
If you have any similar pairs of photos, upload them to the London Old and New Flickr group and we'll feature them in a future post.