Who makes it will depend on which part of the country you are in. They tend to be manufactured to approximate to the local stone from ye olde dayes, so you will be looking for a relatively local company. A nationwide company who offer something similar is
Forticrete which might give you some idea of the type of block. What it most definitely is not...is brick. That's a different material altogether. As has already been said - your best bet is to take the photo to a builders merchant OR find out who built your house, and ask them.