What are these porous bricks in a 1930s house

[dom54]

I'm renovating a room and was wondering what these crumbly bricks are. They were behind the skirting board and spaced roughly every 3 or 4 bricks.

They seem to be of a similar material to the cement block partition walls on the first floor.

The house is 1930s construction in North London. Solid (double brick) external walls and fully rendered on the outside. This is in a first floor room.

Thanks so much for any insight.

 

[^woody^]

For nailing the skirting to.

 

[dom54]

For nailing the skirting to.

Ah that makes sense, the skirting was nailed onto wooden battens when I pulled it off but that must have been redone after it was built.