Iraq Blair Bush
U.S. President George W. Bush (L) meets with British Prime Minister Tony Blair at the G8 summit in Heiligendamm. Reuters

The Chilcot inquiry on the Iraq War has reached an agreement on the "principles that will underpin disclosure" of communications between former British Prime Minister Tony Blair and former US President George Bush.

"I'm pleased to record that we have now reached an agreement on the principles that will underpin disclosure of material from Cabinet-level discussions and communications between the UK Prime Minister and the President of the United States," the head of the inquiry Sir John Chilcot wrote to Cabinet Secretary Jeremy Heywood.

Heywood was due to decide about the publication of some 200 cabinet-level discussions, 25 notes and more than 130 records of conversations between the two leaders that the inquiry had sought to use. He added that the documents under consideration have "raised difficult issues of long-standing principle."

The report from the inquiry was delayed because of confidentiality concerns surrounding the release of the discussions between the leaders.

"Detailed consideration of gists and quotes requested by the Inquiry from communications between the UK Prime Minister and the President of the United States has now begun," wrote Chilcot.

The US reportedly opposed any publication of classified presidential material. In his letter to Heywood, Chilcot reassured that: "Consideration will be based on the principle that our use of this material should not reflect President's Bush views."

Use of direct quotes would also be limited to the "minimum necessary to enable to inquiry articulate its conclusions," Chilcot wrote.

This week, Blair rejected claims that he had intentionally delayed the publication of the inquiry's report.

"I don't know what the reason for the delay is because I'm not in charge of the inquiry and not in charge of the Government.

"All I can tell you it is not for me and I resent the suggestion that it is.

"I have got as much interest as anyone in seeing the inquiry publish its findings and then be able to go out and frankly restate my case and defend my position," he said.

The defence comes after a critical letter sent from the former British Prime Minister to the former US President went missing from White House records.

The letter allegedly has Blair on record saying that he would be "with" Bush on "whatever [he] decide[s] to do" in regard to the Iraq invasion.

No report publication date has been announced.