There are a couple of different ways that manufacturers provide the earth terminal in lampholders. S-Lilley which is a UK base manufacturer use an internal earth connection so there is no terminal seen on the outside of the lampholder.
The switched S Lilley lampholder provide 3 terminals on the inside in both their standard and safer switched lampholders. There is a sprung metal bar that make the contact to the body of the lampholder. This bar can be spurn back to gain access to the earth terminal screw. Being a BC lampholder there is no designation required for the Brown (live) and Blue (neutral) terminals.
Please see here an example of the wiring for these lampholders.