Damage from WWII
As you know, during WWII the Germans bombed the heck out of London. It's interesting because you'll see blocks and blocks of old buildings (pre WWII), and then, right in the middle of the block a few buildings with 1950's or 1960's architecture. Generally, that's where buildings were bombed out and had to be replaced. If you look at this particular building, which is near University College of London, there are little squares on the walls and entry that don't match the rest--this is where they patched up the shrapnel damage. Unfortunately, the patching didn't quite match the building here. There's lots of this all over London.