Trashed: Letwin rebuked for dumping secret files in park bin

Apparent security breach investigated by Cabinet Office and Information Commissioner

A senior minister was forced to issue an apology yesterday after he was caught repeatedly dumping confidential documents in rubbish bins in a London park.

Oliver Letwin, Minister of State in the Cabinet Office, also received a public dressing-down from Downing Street over a series of photographs showing him throwing away paperwork on five occasions over a five-week period.

The apparent security breach – Mr Letwin disposed of correspondence relating to terrorism and national security as well as constituents' private letters – triggered an investigation by the Cabinet Office.

The department was forced to approach the Daily Mirror, which published the pictures and retrieved some of the documents, to establish what material had been discarded by Mr Letwin.

His behaviour is also being scrutinised by the Information Commissioner's Office (ICO), the data protection watchdog, to check whether he breached the law by throwing away the papers in public.

A spokeswoman for David Cameron said there were no "classified documents" in the material dropped in the bins. But she added: "Clearly, it is not a sensible way to dispose of documents. Mr Letwin has agreed he will not dispose of documents in this way again."

As his own department began the inquiry, a spokeswoman for the Minister said: "He sincerely apologises to any concerned constituents and wants to make assurances that he will no longer dispose of copies of documents and constituency correspondence in this way."

An ICO spokesman said: "Keeping personal data secure is a key principle of the Data Protection Act and the ICO takes any breach of that principle very seriously."

Mr Letwin is one of Mr Cameron's closest allies and was an early supporter of his bid to become Tory leader. Despite being regarded as one of the most cerebral of government members, he has also developed a reputation for being accident-prone.

During the 2001 general election campaign he went into hiding after suggesting that a Conservative government had secret plans to cut spending by £20bn; two years later he faced ridicule after calling for asylum-seekers to be shipped to an island "far, far away".

Mr Letwin, the MP for Dorset West, is understood to have thrown away more than 100 papers during early morning strolls in St James's Park in Westminster. He tore up the documents but did not shred them, leaving them legible.

One reproduced by the Daily Mirror was a note from a senior Tory MP about extraordinary rendition – picking up terrorist suspects and flying them around the world for interrogation – to Sir Malcolm Rifkind, the chairman of the Parliamentary Intelligence and Security Committee. Other discarded papers related to the work of the Ministry of Defence, the Home Office and the NHS, as well as operations in Libya, Afghanistan and Pakistan.

Ed Miliband, the Labour leader, said: "It is 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."

Michael Dugher, the shadow minister without portfolio, wrote to Sir Gus O'Donnell, the Cabinet Secretary, calling for an investigation into whether procedures for disposing Whitehall documents had been breached.

He wrote: "Civil servants are subject to disciplinary procedures if the proper processes are not adhered to. It cannot be that there is one rule for ministers and another for everyone else."

Mr Dugher said yesterday: "He and rest of the Tory-led Government are treating the public and their constituents with contempt by handling sensitive correspondence in this cavalier way."