Inside the secret fan campsite behind the O2 Arena

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When a major popstar comes to London fans from all over the world descend on the capital, with many going to extreme lengths to ensure they get near their favourite artist. Queues forming days before concerts have become a feature of many recent arena tours. Now, we've discovered some fans who have gone to particularly extreme lengths... BBC London has visited a secret campsite for Billie Eilish fans along the Thames Path near to the O2 Arena. But why are they there? And are they allowed? Ross Ryan and Eric Anderson discuss what we've found.