Downing Street has refused to bow to mounting pressure to publish the attorney-general's advice on the legality of the war in Iraq.
A Downing Street spokesman said Lord Goldsmith stood by his advice
Tony Blair's official spokesman said Lord Goldsmith's advice - that the conflict was legal - had been given in confidence and would remain secret.
The Lib Dems, Tories and some anti-war Labour MPs want the full advice to be published.
Ex-Tory PM John Major says there is no excuse for not giving full details.
Tony Blair's official spokesman said: "The Attorney General gave his advice as successive attorneys general have given their advice.
"It's precisely because of the need to be able to give frank and free advice that the convention has been that such advice is given in private. That's how it operated, that's what happened."
The Liberal Democrats say Tony Blair should publish Attorney General Lord Goldsmith's advice sooner rather than later, but these demands have so far been rejected by the government.
Foreign Secretary Jack Straw batted away several questions relating to the legality of the war following a speech he gave on European and political reform in the Middle East on Monday.
He told reporters: "As to the position of legal advice, that was fully set out by the attorney general in a statement which he made to the House of Lords."
Mr Straw argued that Saddam Hussein and the Iraqi regime had been in continuing defiance of UN security council resolutions since 1991.
He was speaking after Mr Major told BBC's Breakfast with Frost it was in Tony Blair's interest to reveal Lord Goldsmith's full advice.
Downing Street has refused to comment on newspaper reports that the attorney general changed his advice shortly before the allied campaign began.
According to the Observer and the Independent on Sunday, military officials were concerned that their troops could be prosecuted for fighting illegally.
They allegedly demanded an unequivocal statement that the invasion was lawful from the attorney general.
Mr Major said: "I cannot see any credible or logical reason why - given the circumstances as they now are, given the fact that they have already published a summary of the opinion, given the fact that there is no doubt Lord Goldsmith produced such an opinion - I cannot see at all why that should not now be published.
"This is poisoning the whole political atmosphere."
Shadow foreign secretary Michael Ancram told BBC Radio 4's Today programme: "I think it is right, given the suspicions that are now abroad about the
reasons for going to war, that the attorney general's whole advice is
"This is a matter of crucial importance in terms of public confidence in the
way that governments conduct themselves in the run-up to war."
Sir Menzies Campbell, the Lib Dems foreign affairs spokesman, said it was becoming inevitable that ministers would have to
publish the advice.
"Events appear to be taking an inexorable turn. Sooner or later, one way or another, the whole of the attorney general's advice is going to be published," he said.
"The government would be well advised to do so willingly and not as a last resort."
Speaking on GMTV, Commons leader Peter Hain rejected claims that Lord Goldsmith had been subjected to pressure.
"I think it is a deliberate effort to refocus from the most successful government and prime minister in living memory and to try to sidetrack everyone into what I think has become a very old story," he said.
A Downing Street spokesman said there were no plans to release the attorney general's advice "because of the long-standing convention that advice from government law officers is not disclosed".