Papers covering the UK's exit from the Exchange Rate Mechanism in 1992 have been released after a Treasury document was inadvertently e-mailed to the BBC.
What information to release has led to rows in the Treasury
Documents obtained by BBC News' Freedom of Information Unit revealed internal Treasury debate over what information to make public about "Black Wednesday".
The Financial Times had requested the Treasury assessment of what went wrong.
The Treasury said it regretted that the BBC had revealed some details it had not wanted to be in the public domain.
Black Wednesday, 16 September 1992, was the day Britain crashed out of the ERM - a system for tying the pound and other currencies' values to that of the German mark, and was a precursor to the creation of the single European currency.
Prime Minister John Major and Chancellor Norman Lamont raised interest rates during the day from 10% to 12% to 15% and authorised the spending of billions of pounds in a doomed effort to keep the pound within the range allowed by ERM.
In the end the UK's two year membership of ERM was suspended and the second interest rate reversed. The UK never rejoined the ERM.
The documents were sent to the corporation in an e-mail, apparently by mistake, and they reveal internal rows about how to respond to the Financial Times request.
The papers suggest that 13-year-old financial assessments are among the information officials want to remain private.
Also, there are concerns in the Treasury that the papers could reveal economic spying on France, and also reveal divisions within the then Tory cabinet, the documents suggest.
They also appear to reveal fears that releasing such information could set a precedent for information about Chancellor Gordon Brown's current forecasts and management of the economy.
On Wednesday the papers were released by the Treasury with a guide to exemptions applied to them.
These included the Treasury's regret "that the inadvertent email to the BBC revealed some of the earlier, and in some cases out of date internal discussions among officials about how to implement the FoI Act.
"The BBC release contains some information that the Treasury does not believe should have been put in the public domain," it said.
The guide continued that "certain sections of text have not been included on the grounds that they are not relevant to the question being asked".
Earlier, shadow chancellor Oliver Letwin said there should be "even handedness" about what is disclosed.
"Whatever the rules are for disclosure of things about the present government should apply to past governments," he told BBC Radio 4's Today programme.
"This is supposed to be a Freedom of Information Act, not a Freedom of Propaganda Act."
Mr Letwin said he had had 13 requests for information turned down, including one on development of policy on the euro.
"There needs to be clarity about the kinds of things that can be disclosed and the kinds of things that can't," he said.
But Tony Blair's official spokesman said: "Proper procedures will be followed and these procedures will be overseen by the civil service and the appropriate people."
He added that current ministers "are not permitted to see the papers until they are published".
In recent days, critics have claimed the government has been playing politics with the information laws, when selecting what to make public.
Former Tory Prime Minister John Major has recently denied trying to block the release of papers on "Black Wednesday".
He told BBC News he and former chancellor Norman Lamont had been the victims of "whispering voices" to the press.
The Times reported the publication, under the Freedom of Information Act, had been delayed at their request.