Fred wrote:

This may sound a silly question but; if the pump is double insulated, the
tub and pipework are plastic, what's the earth rod going to be attached to?

To the earth terminal which the OP referred to when he said:

They tub has an earth terminal inside it's control box,

So it does appear to be Class 1 equipment with parts that need earthing.
It would be interesting toe have sight of the installation
instructions; are they on the Web anywhere?

--
Andy