The original Primeval is basically a show about a science-minded group that tracks dinosaurs and other creatures that have slipped into the present day, by way of time/space anomalies called "earthquakes in time".
There are recent photos floating around the internet that allegedly show Holmes on the Primeval: New World set with announced cast member Sara Canning. However, to my knowledge, there has been no official announcement that Holmes has been cast in Primeval: New World.
His IMDb page doesn't list a role in the series either. So, maybe he's a member of the cast; maybe it's a guest spot.
If any S&A readers have info on Holmes' role on Primeval: New World, please feel free to share it with us.