I'm not trying to score points or anything.
That is kind of my problem,
It really shouldn't be.
the installers say it's not needed,
They are responsible for the design. They are responsible for ensuring that the design of the circuits, and the provision (or not) of a high integrity earth complies with the relevant requirements of BS 7671. It is what they are being paid to do. It is their area of professional expertise.
the project manager is complaining I didn't specify it
It is not your job to specify it - it is the job of the person doing the design. It may very well be your job to tell them about the characteristics of the loads, and what sockets you want where, and what granularity of isolation is needed, etc, so that they can do the design properly, but that's not the same thing. You should no more be telling them whether a HI earth is needed that you should be telling them what size cables to use, or what types of breakers are needed for server racks etc.
If the project manager or the QS has issues with the design of the electrical installation then they must raise them with the designers.
If the designers don't know if it is needed then they should be sacked.
As I will be the one who is asked "is this ok?" shortly I'm just canvasing opinion.
That you are having to canvass opinion shows that this is outwith your area of professional expertise, and therefore in a commercial professional context it is outwith your competence to answer.
Absolutely nothing wrong with that, nobody can possibly know everything. You wouldn't expect the electricians to be able to comment on a SAN zoning design, for example.