Tony Blair told US President George W Bush “I will be with you, whatever” eight months before parliament approved the invasion of Iraq, the Chilcot inquiry has found.
The former Labour prime minister also personally agreed to deploy three brigades of combat troops two months before the 2003 invasion, without consulting his senior ministers.
The inquiry, led by Sir John Chilcot, finally released its 2.6m-word report today after seven years, concluding that Britain invaded Iraq before the peaceful options for disarming dictator Saddam Hussein were exhausted.
Tony Blair’s decision to take part in the first invasion and occupation of a sovereign state since World War Two was “not a last resort” and ended in failure thanks to “wholly inadequate” planning for post-Saddam Iraq.
The inquiry said Mr Blair “overestimated his ability to influence US decisions on Iraq” in the months before the war to topple Saddam.
It added that British troops fought bravely but were let down by Whitehall mandarins who failed to supply enough troops or equipment.
British troops ended up in the humiliating position of trading prisoners to stop local militia targeting them.
Politicians had been warned of the chaos that would ensue in Iraq, with the risk of internal fighting and the potential rise of al-Qaeda “explicitly identified before the invasion”.
The inquiry notes that the government relied on flawed intelligence assessments of the threat from Saddam from the Joint Intelligence Committee.
But Tony Blair and foreign secretary Jack Straw also made statements on the danger from Weapons of Mass Destruction (WMDs) that were not supported by intelligence findings.
The inquiry set out a note sent by Mr Blair to President Bush on 28 July 2002, the summer before the invasion of Iraq.
Mr Blair wrote: “I will be with you, whatever. But this is the moment to assess bluntly the difficulties. The planning on this and the strategy are the toughest yet.”
The prime minister said getting rid of Saddam was “the right thing to do”, adding: “He is a potential threat. He could be contained. But containment… Is always risky. His departure would free up the region. And his regime is…brutal and inhumane.”
In the note, Mr Blair also talked about the importance of getting international support for an attack on Saddam, including making progress in the peace process between Israel and the Palestinians, as well as getting authority from the UN, and changing public opinion in the UK, Europe and the Arab world.
On building the public case for toppling Saddam, Mr Blair said Britain and America should “recapitulate all the WMD evidence; add his attempts to secure nuclear capability; and, as seems possible, add on the al-Qaeda link, it will be hugely persuasive over here”.
In fact, the Joint Intelligence Committee had assessed the risk of co-operation between Iraq and al-Qaeda as “unlikely” and said there was “no credible evidence” of WMDs being handed to terror groups.
The inquiry notes that Mr Blair had in fact been warned that military action against Saddam would “increase the threat from al-Qaeda to the UK and to UK interests”.
“He had also been warned that an invasion might lead to Iraq’s weapons and capabilities being transferred into the hands of terrorists.
The Chilcot inquiry said Mr Blair “overestimated his ability to influence US decisions on Iraq”.
It concludes: “The UK’s relationship with the US has proved strong enough over time to bear the weight of honest disagreement. It does not require unconditional support where our interests or judgements differ.
The report also stresses “the importance of collective Ministerial discussion which encourages frank and informed debate and challenge”.
On several important occasions Mr Blair acted without Cabinet discussion.
On 17 January Mr Blair agreed to deploy a UK division with three combat brigades for possible operations in southern Iraq, without discussing the decision with senior ministers.
Chilcot notes that the legal justification for going to war rested on the Attorney General Lord Goldsmith asking Tony Blair for confirmation that there had been “material breaches” of UN resolution 1441.
Mr Blair’s private secretary for foreign affairs, Matthew Rycroft, wrote to Lord Goldsmith’s office on 15 March saying: “This is to confirm that it is indeed the Prime Minister’s unequivocal view that Iraq is in further material breach of its obligations…”
But the inquiry concludes that: “It is unclear what specific grounds Mr Blair relied upon in reaching his view.”
The prime minister made his mind up about the evidence that Iraq was breaching the UN resolution on weapons inspections without seeking advice or consulting senior ministers.
Mr Blair then let Lord Goldsmith take the lead in explaining the government’s legal position to parliament on 17 March 2003, without explaining his hand in it.
The Chilcot Inquiry concludes that parliament was not misled, and there was no “side deal”, as alleged by Clare Short in evidence to the inquiry, but Cabinet members should have been made aware of the legal uncertainties previously noted by Lord Goldsmith.
Chilcot notes that Britain’s armed forces successfully took Basra during the invasion and helped topple Saddam in less than a month.
But “wholly inadequate” planning meant British forces were overstretched in the occupation that followed.
“The scale of the UK effort in post-conflict Iraq never matched the scale of the challenge. Whitehall departments and their Ministers failed to put collective weight behind the task.”
Delays in providing vehicles more heavily armoured than the lightweight Snatch Land Rovers “should not have been tolerated”, the report adds.
The inquiry lays the blame for this at the door of the Ministry of Defence, which “was slow in responding to the threat from Improvised Explosive Devices, but it does not blame individual people or departments within the MoD.
By 2007 British forces in Basra were reduced to exchanging detainees with dominant local militia groups to try to stop attacks.
The inquiry said: “It was humiliating that the UK reached a position in which an agreement with a militia group which had been actively targeting UK forces was considered the best option available.
“The UK military role in Iraq ended a very long way from success.”