A British government minister has been photographed leaving the Prime Minister's residence holding a confidential document that welcomes the departure of Afghan President Hamid Karzai.
A briefing paper clearly visible in the hand of International Development Secretary Andrew Mitchell said the Britain should publicly and privately approve Mr Karzai's decision not to seek a third term as president in 2014.
In response, Foreign Secretary William Hague said the memo was ''pretty low level'', adding ''these things happen''.
Mr Mitchell was photographed leaving Downing Street following a meeting of the National Security Council - in which ministers discussed Libya, Afghanistan and a range of other issues.
The BBC's political correspondent said Mr Mitchell immediately realised he had mistakenly displayed confidential briefing papers and told an aide ''it is nothing top secret''.
The document says:
''Note that Karzai has publicly stated his intention to step down at the end of his second term as per the constitution. This is very important.
''It improves Afghanistan's political prospects very significantly. We should welcome Karzai's announcement in private and in public.''
It goes on to say:
''Afghan perceptions of violence are very important for their confidence in their future, and for their readiness to work for the Afghan government.''
The BBC reports the document also discusses reforms to Afghanistan's banking sector and a planned IMF visit to the country.
Mr Karzai was re-elected to a second five-year term in 2009 after an election which was marred by accusations of fraud and vote-rigging.
Under the terms of the Afghan constitution, Mr Karzai is not allowed to stand for a third term - which means he will stand down in 2014.
There had been speculation he would try to continue in office beyond that date but he has confirmed he will not be seeking a third term.
Mr Karzai's relationship with Britain and the United States has often been fraught, with critics urging him to do more to tackle corruption within his government.
Not the first
Mr Mitchell is not the first person to be caught unawares by photographers outside No 10.
Former senior Metropolitan Police officer Bob Quick was mistakenly revealed a secret terrorism document as he arrived at Downing Street in 2009.
He subsequently resigned, saying his position was ''untenable''.
In other similar cases:
Treasury minister Danny Alexander was pictured last year holding a memo detailing the forecast scale of public sector job cuts.
In 2009, the then-Labour Cabinet minister Caroline Flint inadvertently displayed a document which talked of a ''property crisis''.
