Cabinet Office minister Oliver Letwin broke the law when he was caught regularly dumping sensitive official documents in a London park bin, the Information Commissioner has found.

Following his breaking of the Data Protection Act, Information Commissioner Christopher Graham has now issued a warning to Letwin - the Conservative MP for West Dorset - that he faces "formal enforcement action" if he continues to carelessly throw away letters and papers.

Such action could include legal action being brought against the MP and a large fine. Letwin has now signed a written commitment pledging to dispose of his files in a secure manner, which can be read here.

Graham said: "Constituents entrust their MP with all sorts of personal information and should never expect the details of the concerns they've raised in confidence to end up in a park bin for anyone to see. It is clear that Mr Letwin has learned from this incident and we're pleased that he has co-operated fully."

Letwin apologised last month after he was photographed by the Daily Mirror disposing of papers in a bin at St James's Park, near Downing Street, on five separate occasions.

The Mirror reported the MP had dumped more than 100 papers dating from July 2010 to September 2011. These documents included correspondence from constituents and five intelligence and security committee letters.

The documents included details of UK involvement in rendition, al Qaida links to Pakistan, and details of a constituent's hospital treatment. The Commissioner found that letters and emails contained the names, addresses and contact details of around 20 individuals.

Letwin has promised to ensure that any documents containing personal data are disposed of in a secure manner. He will now also make sure he complies with the Cabinet Office's data handling guidance.