Extracts from a record of a phone call between Tony Blair and George W Bush on the eve of the Iraq War must be released, a tribunal has ruled.
The Foreign and Commonwealth Office (FCO) was ordered to disclose parts of a note detailing a conversation between the two leaders on March 12 2003.
Mr Blair and Mr Bush are believed to have used the call to discuss a TV interview given by then-French president Jacques Chirac two days earlier about ongoing talks on Iraq at the United Nations.
Former British government ministers have blamed Mr Chirac's comments for the breakdown of efforts to secure a second UN Security Council resolution specifically authorising military action against Saddam Hussein's regime.
The FCO said publishing the record of the conversation between Mr Blair and Mr Bush would cause "significant damage" to Britain's relationship with the US. But the information rights tribunal largely upheld an earlier ruling by the Information Commissioner that parts of the notes can be released.
A panel chaired by tribunal judge Professor John Angel concluded: "The circumstances surrounding a decision by a UK government to go to war with another country is always likely to be of very significant public interest, even more so with the consequences of this war."
The tribunal ordered that an edited version of the note should be released within 30 days. An FCO spokesman said: "The FCO is obviously disappointed by the decision of the tribunal. We will want to study the terms of the judgment more closely over the coming days."
Former foreign secretary Jack Straw told the Chilcot Inquiry into the Iraq War in January 2010 that Mr Chirac's March 10 2003 interview killed off hopes of a diplomatic solution to US and UK concerns about Iraq.
He said: "This was the great Chiracian pronouncement. Whatever the circumstances, he says, La France will veto." But Britain's then-ambassador to Paris, Sir John Holmes, told the inquiry in June 2010 that he interpreted president Chirac's words differently. "It was ambiguous," he said.