I did 6 months working Southampton last year and was in and out of gate 10 several times a day, not with containers but a curtainsider collecting freight around the docks. During that time I was not stopped once either in or out, and was never given any document that looked anything like a gate pass from the places I loaded.
Working Tilbury now and it’s like a different world, I even know the security guess by name now and still get stopped!!