The Cabinet Office will have to give a new Freedom of Information response after it wouldn't hand over information about the Area Plan for the North and West.
Information Commissioner Dr Alexandra Delaney-Bhattacharya says the government redacted information after being asked for specific documents regarding the blueprint for Island development.
It had already provided more information after an internal review.
But the ICO says it didn't properly consider data protection principles, and lacked evidence it had considered what it called vexatious elements.
It must now re-process the request and provide a new response.
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