She'll be right

I guess it depends on what that base block is the base of?

I would not worry about that

Linux

Its probably the most valuable asset you own, if I was you I would consult with a qualified registered master builder 

dt:

 

Its probably the most valuable asset you own, if I was you I would consult with a qualified registered master builder 

 

If I were to hazard guess I would say that has been hit in the recent years, looks like water is getting in. Is the wall on the other side still hollow sounding or damp?

I would speak with a MB regarding this. Will most likely need to remove the plaster.

It doesn't appear structural but it looks as if the whole front of that block has been cracked and slightly moved away from the rest of the block and the plaster may have slightly shifted under it.

JayADee: If it were mine I'd be wanting to get that plaster off for a good look then go from there. If that's a block you will be able to remove it and replace it with an unbroken one.

As a corner block it should have reinforcing running through it vertically (and possibly horizontally) and should also be concrete filled - which makes the damage look odd and worth inspecting.

So I would definitely get it looked at both from a structural and weather tightness POV.

I'd get it fixed, because the more water that penetrates into that crack, the worse it could get.