Croydon Council said its plan to use an underground footway in Purley to hold around 600,000 litres of water was approved after its "primary" pond at Purley Depot overflowed on Friday night.
This has not been an easy decision to take but it has become increasingly clear over the past few hours that we have no alternative if we are to protect people's homes and businesses from being flooded.
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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.