'If my soldiers went to jail and I did, some other people would go with me,' said Boyce.

In his most detailed explanation yet of why he demanded an unequivocal assurance from lawyers that the war was legal, he said: 'I wanted to make sure that we had this anchor which has been signed by the government law officer ...

'It may not stop us from being charged, but, by God, it would make sure other people were brought into the frame as well.'

Pressed by The Observer on whether he meant the Prime Minister and the Attorney General, Boyce replied: 'Too bloody right.'

The admiral added that he had never been shown the crucial 7 March advice by Goldsmith that questioned whether the war was legal. He had only been given a later assurance of legality, which contained none of the caveats. It was only after he questioned Number 10 about legal 'top cover' that he was given Goldsmith's opinion.

Boyce has consistently said he believed the war was legal and morally justified. But, asked whether the government had provided him with the legal cover necessary to avoid prosecution for war crimes, he replied: 'No.'

He added: 'I think I have done as best as I can do. I have always been troubled by the ICC. Although I was reassured ... when [discussions over signing up to the ICC were] going through Whitehall about five years ago, I was patted on the head and told: "Don't worry, on the day it will be fine." I don't have 100 per cent confidence in that.'

In a further damaging development for the government, documents leaked to a Sunday newspaper appeared to show that Tony Blair was considering military action to topple Saddam Hussein as early as 2002.

According to minutes from a meeting held in Downing Street on 23 July, obtained by the Sunday Times, the assumption had been made that 'the UK would take part in any military action' initiated by the United States.

Blair said it 'would make a big difference politically and legally if Saddam refused to allow in the UN inspectors.' He added: 'If the political context were right, people would support regime change.'

The minutes confirm that the Attorney General did not believe regime change was a basis for military action.

A further confidential document leaked this weekend is the Foreign Office legal opinion that expressed grave doubts about the legality of war without a second UN resolution.

An Observer investigation into the legal ramifications of the war also reveals that Goldsmith's advice authorising war was shaped after meeting the five most powerful Republican lawyers in the Bush administration, in February 2003.

These included Alberto Gonzales, Bush's controversial chief legal adviser who has been at the centre of the Abu Ghraib prison abuse scandal. Gonzales once famously described elements of the Geneva Conventions on the treatment of prisoners of war as 'quaint'.

The four other lawyers were William Taft IV, chief legal adviser to the then Secretary of State Colin Powell; Jim Haynes, chief legal adviser to Donald Rumsfeld in the Pentagon; John Bellinger, chief legal adviser to Condoleezza Rice; and the then US Attorney General, John Ashcroft.

Speaking to The Observer from his Virginia home, Taft explained how the US argument that a second UN resolution was not needed before invading Iraq was put to an undecided Goldsmith. Taft said: 'I will say when we heard about his statement in Parliament [on 17 March] ... what he said sounded very familiar.'

Last week, the government was forced to disclose the 13-page legal document, drawn up by Goldsmith on 7 March, following leaks to the media. This revealed the importance of Goldsmith's trip to Washington, which provided the backbone of the 'reasonable case' for war without a second UN resolution.

In paragraph 23 of his 7 March advice, Goldsmith said: 'I was impressed by the strength and sincerity of the views of the US administration which I heard in Washington.'

In contrast to his 'unequivocal' legal authority for war given to Parliament 10 days later, this document revealed Goldsmith's misgivings over the legality of the war without a UN resolution.

Neither ministers nor Parliament were shown the complete advice, leading to claims they were misled into backing the war. The revelation that the man in charge of Britain's armed forces was also not shown the advice has been described as 'staggering' by Philippe Sands QC, an expert in international law.

Boyce told The Observer: 'I didn't see it - it was not copied to me.'

Last night, government sources confirmed that Goldsmith met the five Washington lawyers on 11 February 2003. A spokeswoman for the Attorney General said he had travelled to Washington to listen to American opinion and had not been pressured to change his view on the war.