That rather grim lump of concrete is one of the country's newest Grade II listed buildings. It's the Block C group of buildings at Bletchley Park, where the Nazi codes were crunched.
Block C consisted of toughened, soundproofed buildings, which housed the actual machines that did the WWII number crunching. It's the world's first IT room. It's also now virtually entirely derelict, but as we've previously mentioned, the Bletchley Trust is currently raising funds to restore this depressing lump to its former... glory.
Tourism and Heritage Minister John Penrose said: “It’s important the fabric of the building as well as the history surrounding the work of so many people inside those four walls is protected for future generations, and Block C clearly merits the extra protection against unsuitable alteration or development that listing provides." [DMCS via Guardian]