Hundreds of people were caught at a suspected rave under a railway arch in Hackney on the weekend.
The Met Police were called at 1.30am on Saturday (January 23) to reports of an unlicensed music event in Nursery Road.
Officers say there was loud music and a "significant number" of people inside.
Attendees were "uncooperative", officers claim, and the doors then padlocked from the inside.
When officers finally forced entry with their backup, which included public order officers, a dog unit and a helicopter, they said they saw some 300 people inside.
Many fled the scene - dozens allegedly scaled fences and others forced open a gate.
However, 78 people were issued with £200 fines, totalling £15,000.
Ch Supt Roy Smith, who attended the incident, said: "Officers were forced, yet again, to put their own health at risk to deal with a large group of incredibly selfish people who were tightly packed together in a confined space - providing an ideal opportunity for this deadly virus to spread."
He said anyone who attends illegal parties can expect to be fined, not just the organisers.
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