There are a couple of different ways that manufacturers provide the earth terminal in lampholders. S-Lilley which is a UK based 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 thin metal bar that make the contact to the body of the lampholder from the earth terminal. This bar can be bent backwards 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.
However the Earth (Green/Yellow) MUST be connected to the center terminal.
Please see here an example of the wiring for these lampholders.
If you have the BC lampholder with the external earth block the earth cable still runs up inside the lampholder and not externally as some may think.
Again it does not matter which way the Live ( Brown) and Neutral (Blue) go.
See the image below on how to connect these styles of lampholder up.