The UK government's former top lawyer appears before the inquiry into the Iraq War on Wednesday, with questions set to focus on why he changed his view that the conflict did not break international law.

Three days before the March 20, 2003 invasion, Attorney General Peter Goldsmith told parliament that the use of force was legal on the basis of resolutions previously passed by the United Nations.

However declassified documents and evidence given to the inquiry into Britain's role in the war show that Goldsmith had not given such explicit advice just 10 days earlier.

Critics of the war have long suspected that Goldsmith was pressured into changing his mind by then Prime Minister Tony Blair.

On Tuesday, the two most senior legal advisers at the Foreign Office in the run up to the invasion said they believed that the use of force without a specific mandate from the UN meant the military action was illegal.

According to previously secret documents made public on Tuesday, Goldsmith expressed doubts about whether there was legal justification for war under resolution 1441, passed by the UN Security Council in November 2002.

Notes of a telephone call between then Foreign Secretary Jack Straw and Goldsmith shortly after that resolution was passed, indicated that he was not 'optimistic' it could be used to justify military action should Iraq breach its terms.

'He was in fact pessimistic as to whether there would be a sound legal basis in such a situation for the use of force against Iraq,' the note said.

As late as March 7, 2003 when he gave detailed advice to Blair, he cautioned that a second UN resolution was the safest course of action.

By March 13, two days after a meeting with Blair and his team, Goldsmith had decided this second resolution was no longer necessary.

'The Attorney General confirmed that, after further reflection, he had come to the clear view that on balance ... there was a lawful basis for the use of force without a further resolution beyond resolution 1441,' a note by one of Goldsmith's senior aides David Brummell said.

Giving evidence on Tuesday, Brummell said Goldsmith had not come under pressure from Blair and ministers to change his advice.

He said Goldsmith had been asked at the March 11 meeting to provide a clear statement on whether force would be lawful, and he had then reached his conclusion.

Michael Wood, who was the Foreign Office's top legal adviser at the time, told the inquiry on Tuesday he disagreed with Goldsmith and said he believed there was no legal basis for war.

Elizabeth Wilmshurst, who was Wood's deputy and quit over the invasion she said amounted to a 'crime of aggression', said it was 'lamentable' and 'extraordinary' that the government had waited so long before seeking the Attorney General's advice.

'For the attorney to have advised that the conflict would have been unlawful without a second resolution would have been very difficult at that stage, I would have thought handing Saddam Hussein a massive public relations advantage,' she said. – Reuters