Cabinet Office minister Oliver Letwin has apologised after being caught dumping sensitive official documents in a park bin.
Mr Letwin was photographed by the Daily Mirror disposing of papers - including correspondence on terrorism and constituents' private details - near Downing Street on five separate occasions.
Labour accused the Tory policy chief of treating the public "with contempt" by handling material in a "cavalier" fashion. Downing Street admitted the behaviour had not been "sensible" - but also stressed that none of the information was classified.
According to the newspaper, there were more than 100 papers dating from July 2010 to September 2011, and included five Intelligence and Security Committee (ISC) letters.
In one, MP Andrew Tyrie reportedly tells ISC chairman Sir Malcolm Rifkind the committee "failed to get to the truth on UK involvement in rendition".
Another discarded document was said to refer to al Qaida links to Pakistan.
David Cameron, his Liberal Democrat deputy Nick Clegg and Chancellor George Osborne are all said to feature, as are organisations including the Ministry of Defence, the Home Office and the NHS.
The West Dorset MP reportedly tore up the documents but did not shred them, leaving them still legible.
In one picture Mr Letwin was dropping papers into a bin while talking on a mobile phone, and in another he appears to hand some to a passing cleaner.
A spokeswoman for Number 10 said that the Cabinet Office was "looking into" whether any secret material had been compromised.
"Our understanding is that there were no classified documents," she said. "Most of the business which Mr Letwin does in the park is constituency-based.
"In the light of what has been reported, the Cabinet Office is looking into it."
Asked what the Prime Minister's view was, the spokeswoman said: "Clearly, it's not a sensible way to dispose of documents.
"Mr Letwin has agreed he will not dispose of documents in this way again."
Labour leader Ed Miliband said: "I think it's treating important papers with contempt, really."
He added: "It's very strange behaviour. I think most people would think, actually, you're dealing with sensitive papers, you're dealing with sensitive correspondence, you should treat it in a sensitive way.
"This is another example of there being one rule if you're in the Cabinet and seemingly another rule for everybody else."
Mr Letwin's behaviour is also being examined by the Information Commissioner amid suggestions he may have breached the law by dumping the paperwork.
However, the minister insisted the story was merely "embarrassing" and no government or classified information had been put at risk.
"I was walking around dictating responses and simply wanted to make sure the pieces of paper were not weighing me down," he said.
"I have to apologise to constituents who have written to me because, on reflection, I shouldn't have disposed of them (the papers) in that way."