Here, again, are these people 'crammed' onto the beach.
Evidently, some among them behaved appallingly. Some got drunk on cheaper supermarket booze, possibly because the pubs are closed. Some urinated or defecated inappropriately because either the loos were closed or there were too few of them. And they were, in the Great British Tradition, drunk.
I'd bet the vast majority did the SD you can see in my photo, didn't leave their trash, and didn't shit on the beach.
I reckon it took one understandably disgusted beach cleaner to find one turd in one burger box in order for the 'good people' of Bournemouth, as represented on here, to assume the beach became an open, running sewer.