Roger Harding from Shelter says "It's truly shocking how many people are living with the threat of becoming homeless''
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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.