The stark terms in which the US was warned that invading Iraq without a second UN security council resolution could cost Tony Blair his premiership have been revealed in newly released documents.

Blair’s foreign policy adviser, David Manning, warned Condoleezza Rice, the then US national security adviser: “The US must not promote regime change in Baghdad at the price of regime change in London.”

The meeting between the two took place before Blair visited the US president, George W Bush, at Camp David on 31 January 2003, two months before the Iraq invasion.

While the US had not yet decided on a second security council resolution, Blair’s objectives at Camp David were to convince the US a second resolution was “politically essential for the UK and almost certainly legally essential as well”, and to hold off from a February invasion until the end of March, according to a briefing note to Blair from Manning released by the National Archives in London.

In a separate 29 January memo to Blair marked “secret – strictly personal, very sensitive”, Manning said he told Rice: “A second resolution is a political necessity for you [Blair] domestically. Without it, you would not secure cabinet and parliamentary support for military action. She must understand that you could be forced from office if you tried. The US must not promote regime change in Baghdad at the price of regime change in London.”

Manning wrote: “I said that Bush could afford to gamble. He wanted a second resolution but it was not crucial to him. He already had congressional authority to act unilaterally. This was quite different from the situation you were facing.

“Condi acknowledged this but said that there came a point in any poker game when you had to show your cards. I said that was fine for Bush. He would still be at the table if he showed his cards later. You would not.”

The Americans were becoming increasingly impatient with the unwillingness of France and Russia – which both had a veto on the UN security council – to agree a resolution so long as UN inspectors were unable to find any evidence of Saddam Hussein’s weapons of mass destruction, the supposed justification for war.

After Bush’s annual State of the Union address to Congress, shortly before Blair’s visit, the UK’s Washington ambassador, Christopher Meyer, warned that the options for a peaceful solution had effectively run out.

Meyer described Bush’s message on Iraq by this point as “messianic”. It was now “politically impossible” for Bush to back down from war “absent Saddam’s surrender or disappearance from the scene”, he wrote.

Bush’s State of the Union address had closed off any room for manoeuvre, Meyer informed London: “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 another cable the previous month, he said of Bush: “His view of the world is Manichean. He sees his mission as ridding it of evil-doers.”

In the end, the US and UK abandoned their efforts to get agreement on a resolution, claiming the French president, Jacques Chirac, had made it clear he would never agree.

In another briefing note before Camp David, the Ministry of Defence warned: “The loosening of Saddam’s grip on power may give rise to significant levels of internecine violence.”

One of the key findings of the Chilcot report was that Blair had ignored warnings on what would happen in Iraq after invasion, and it rejected Blair’s claim that the subsequent chaos and sectarian conflict could not have been predicted.