What are these interlocking blocks ??

Hi all, we have a wall in our garden made out of some mortarless interlocking concrete blocks and I would like to find out what they are and try and get some more. They are flush on one side and look like hanging tile on the other and simply stack together mortar free. The previous owner of the house suggested they were agricultural (used for animal enclosures on farms etc.). Does anyone know what they are? Photos below.

Thanks
Toby

Ps. Bedfordshire in case that helps.

 

Thanks & yes, but specifically which / who's mortarless blocks do I have?