I believe so.
To what would the earth core be connected on a plastic lampholder?
I have heard the argument that "all subcircuits shall incorporate a circuit protective conductor" but in my view a lighting festoon is a double insulated appliance and not a suibcircuit.
What would however be poor pratice, and contary to regulations, would be to fit a standard 2 pole and earth trailing socket to the far end of the festoon lighting.
This is often done in order to facilitate the connection of a second lighting festoon, if the socket is only used for this purpose then no harm arises.
In practice though there is a substantial risk that a portable tool, perhaps requiring an earth, would be plugged into this unearthed outlet.
