THE latest delay in the inquiry into the Iraq war is "intolerable" and the public has a right to know the full story behind Britain's involvement, former Liberal Democrat leader Sir Menzies Campbell has said.

Inquiry chairman Sir John Chilcot has requested that more than 150 letters and conversations between former prime ministers Tony Blair and Gordon Brown and then-US president George Bush should be declassified, but no agreement has been reached with the Government's most senior official.

Prime Minister David Cameron said the process needed to be handled "sensitively" but hoped that the consideration of the papers could be concluded as soon as possible.

But Sir Menzies, who as the party's foreign affairs spokesman was one of the most vehement critics of the war, said: "It is ­intolerable that the work of the inquiry should be thwarted at this late stage."

The North East Fife MP added: "Sir John Chilcot and his colleagues have now been engaged in this for more than four years.

"The Iraq adventure is one of the most serious failures of government policy in the last 50 years. There is every reason to require that, in the public interest, the full story should be told."

The latest hitch in the process centres on criticisms the inquiry's report will make of "relevant ­individuals" - thought to include Mr Blair - and the evidence to be published to support the findings.

The task of informing individuals about provisional criticisms that will be made of them - known as Maxwellisation - has been delayed because of the failure to reach agreement with the country's most senior civil servant, cabinet secretary Sir Jeremy Heywood, about the disclosure of sensitive documents.

In a letter to Mr Cameron explaining the delay, Sir John said discussions between the inquiry team and Sir Jeremy started earlier this year on the "most difficult categories" of material.

He wrote: "Indeed, beginning in June this year the inquiry has submitted 10 requests covering some 200 cabinet-level discussions, 25 notes from Mr Blair to president Bush and more than 130 records of conversations between either Mr Blair or Mr Brown and president Bush."

He added that "it is regrettable that the Government and the inquiry have not reached a final position on the disclosure of these most difficult categories of document".

Sir John added: "I and my colleagues have agreed that the inquiry should not issue those provisional criticisms without a clear understanding of what supporting evidence will be agreed for publication.

"The inquiry has therefore contacted the relevant individuals to notify them that the Maxwellisation timetable has been delayed and that we are not yet able to confirm when we will be in a position to provide them with the material that they expect."

In his reply to Sir John the Prime Minister said he was "aware of the scale of the task declassification has presented to a number of Government departments" and the Cabinet Office and other ministries had been asked to deal with requests relating to "several thousand documents".

He added: "I appreciate that consideration of the disclosure requests for the remaining ­sensitive categories of information must be handled sensitively and carefully but I hope that consideration of the final sets of papers can be concluded as soon as possible."

Sir Menzies said the public had a right to expect the inquiry's report to be published.

"The chairman's letter to the Prime Minister makes it clear that there are individuals whose conduct may be subject to criticism," he said.

"It is unfair on them that this matter should be dragged out, but much more to the point it is wholly against the public interest that the full story should not be told."