An FOI request for details about the conversion of the North London Line between Stratford and Canning Town to a Docklands Light Railway line (link below.)
http://www.dft.gov.uk/foi/responses/2007/july2007/nll/nll

One of the arguments against disclosing some of the information was :

"the need for 'free thinking space' for policy determination, without the fear that policy proposals will be held up to ridicule or public criticism."

So if civil servants (or indeed ministers) prove their incompetence by proposing something that is clearly absurd , then the public should not find out about this.......

Further quote :

"I apologise that your name and address was communicated to a third party. This arose in the course of a consultation exercise undertaken because the FOI Act request embraced information held by the Department for Transport received from third parties. We have now clarified our FOI case handling procedures to ensure that this does not occur in the future. A copy of this letter without your name and address will be published on the DfT website shortly."