It would have been “politically impossible” to stop President Bush from invading Iraq, as he believed he was on a “crusade against evil”, new records show.

Newly declassified UK government files show Sir Tony Blair was warned by his US ambassador that George W Bush was determined to overthrow dictator Saddam Hussein, in the months before the invasion of Iraq.

Sir Tony, who was prime minister at the time, was trying to encourage the US president to use diplomatic means to change the situation in the Middle Eastern country, and flew to Camp David in January 2003 to make the case, just two months before the joint US-UK invasion.

The UK government was also hoping the United Nations Security Council would agree a new resolution specifically authorising the use of military force against Iraq.

But the files, made public for the first time, show that Sir Tony’s ambassador, Sir Christopher Meyer, warned him it would be “politically impossible” to sway Mr Bush away from an invasion unless Hussein surrendered.

The documents, released by the National Archives at Kew in west London, show Sir Christopher also wrote that Mr Bush believed himself to be on “a crusade against evil to be undertaken by God’s chosen people”.

Sir Tony’s foreign policy adviser, Sir David Manning, told the PM that when he met Mr Bush, he should make the point that a new diplomatic resolution was “politically essential for the UK, and almost certainly legally essential as well”.

But the White House was becoming increasingly impatient at the unwillingness of France and Russia – both of whom held a veto – to agree a resolution so long as UN inspectors were unable to find any evidence of Iraqi weapons of mass destruction, the supposed justification for war.

Sir Christopher warned Sir Tony shortly before his visit to see Mr Bush in January 2003 that options for a peaceful solution in Iraq had effectively run out.

He wrote: “It is politically impossible for Bush to back down from going to war in Iraq this spring, absent Saddam’s surrender or disappearance from the scene.

“If Bush had any room for manoeuvre beforehand this was closed off by his State of the Union speech.

“In the high-flown prose to which Bush is drawn on these set-piece occasions, he said in effect that destroying Saddam is a crusade against evil to be undertaken by God’s chosen people.”

In a cable sent the previous month, Sir Christopher said that much of the impulse for deposing Hussein was coming from the president, a born-again Christian, who was scornful of what he saw as the “self-serving” reservations of the Europeans.

“His view of the world is Manichean. He sees his mission as ridding it of evil-doers. He believes American values should be universal values,” Sir Christopher stated.

“He is strongly allergic to Europeans collectively. Anyone who has sat round a dinner table with low-church Southerners will find these sentiments instantly recognisable.”

In the end, Sir Tony and Mr Bush abandoned efforts to get a new Security Council resolution, blaming French President Jacques Chirac for refusing, and launched the invasion of Iraq anyway.

Lobbying from Mandelson and anger at the French

Among the new files, there are also a number of other revelations. These include:

• Current UK ambassador to the US, Sir Peter Mandelson, was so desperate to get back into government following his second resignation from Sir Tony’s government that he asked Lord Birt, a policy adviser to Downing Street, to write to the prime minister in 2003, asking for him to receive a role – four months before Sir Peter was appointed as the UK’s next European commissioner
• Sir Tony was furious at French president Jacques Chirac’s efforts to undermine pressure being put on Zimbabwean dictator Robert Mugabe by the UK in 2003, over growing violence caused by a policy of driving the remaining white farmers from their lands in the African nation
• The prime minister also insisted on changing the rules around which parties can lay wreaths at the Cenotaph on Remembrance Sunday in a bid to protect the Northern Irish peace process in 2004, despite warning this could create an “adverse reaction” from the SNP and Plaid Cymru