Which festival will be the first to charge camping according to the square feet occupied, it will have to happen soon.

Cambridge already does.

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The charge is for tent space not the people inside, so camping costs may be shared. One camping ticket entitles you to a plot large enough for a 2/3 berth tent space of max size 4.5m x 3.5m inc guy ropes, measured from the longest to the widest point. To camp, you must purchase a Full Festival ticket and sufficient Camping tickets for the size of your tent for the campsite of your choice