Houses in SE26 used by War Ministry WW2

[cASIOCZ3000]

I have been told by the freeholder of my flat on crystal palace park road, who has lived there since 1969, that the house was used by the War Minstry in WW2, and that the W etched into one of the bricks indicates this. Has anyone ever heard of this marking of bricks used by the army/war minstry? I cant find anything on line. He also told me about the house torn down on the part of Crystal Palace Park, called the grove which my flat faces. It seems it was occupied by squatters in the 60's having been abandoned, and the damage was such that it was torn down in circa 1977. Sad. Has anyone got a good resource for history of crystal palace park road?