Brittany Ferries Poole check-in?

I turned up middle of the night for the morning ferry, did the weigh bridge and got waved through the gate, but is there an actual check desk I need to find now i’m in the lanes like there is at Portsmouth?

You posted this quite a while before I saw it so I assume you are well on your way now. I have not used that ferry terminal in a long time but there used to be a check in desk, near the car assembly area.