The part (circled in red) has snapped off - I think it belongs to the entry fill valve. I have placed the knife in there to stop the cistern from filling and overflowing.
Should I try and super glue the black bit attached to the metal connector (at the bottom of the red blob, you can see the black plastic bit that has snapped off)?
Or, should I replace the entire unit? If so anyone know what this unit is and where I can get it from?