The Liberal Democrats have attacked the "utter confusion" at the heart of government following the revelation that the attorney general may never have provided a full legal brief on the legality of the Iraq war.

Lord Goldsmith published a written statement outlining his thinking in the run up to the war with Saddam Hussein.

And the Butler report on intelligence matters said that Number 10 had sought the attorney general's legal advice in writing, which was then provided in a formal minute.

But giving evidence to MPs on Thursday, top civil servant Sir Andrew Turnbull appeared to indicate that the summary given to the Cabinet was the full extent of Lord Goldsmith's advice.

"There is no other version," the Cabinet secretary told the Commons public administration select committee.

"There is not a longer version of that advice."

He added: "This is the definitive statement of his views."

The disclosure could explain why the government has repeatedly refused requests to publish the full text of the legal advice.

Lib Dem leader Charles Kennedy said it was an "astonishing revelation" which suggested "utter confusion at the heart of government".

"The prime minister must now clarify the situation which is undermining public trust," he added.

"He must provide a clear statement about what took place regarding the legal advice.

"Can it really be true that the legal basis on which we went to war consisted of a parliamentary answer and not a full legal opinion?"