Black/Dark blue crumbly bricks on internal wall

[spada01]

I'm doing a house refurb and the structural engineer has approved removing two walls. On taking off the plaster they aren't standard brick, but some sort of dark blue/black brick that's very crumbly and weak.

Anyone any idea what these are?

It's a 1930s house in West London and all the external walls are standard brick.

 

[PrenticeBoyofDerry]

Could be an engineering brick, they come in many colours.
Have you a picture you can upload?