Jon Griffin from the Enviroment Agency said: "This site has an absolute limit of 5,000 tonnes of waste at any one time allowed to be stored in there. They've gone way over that for quite some time.
"We've told them to clear the site basically if all the waste and that is the only way to stop the fires that keep breaking out and causing misery for the local residents. This is the worst site I've seen in my career"
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The venue says it is in contact with promoters about a final decision, following the terror attack at the singer's concert on Monday.
Soldiers will replace armed police at many sites after security experts warned the Government that another terrorist attack may be imminent.
The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.