Exclusive: Leadership frontrunner tells Guardian he will apologise for ‘deception’ in run-up to 2003 invasion and to Iraqi people for suffering

The Labour leadership frontrunner Jeremy Corbyn is to issue a public apology over the Iraq war on behalf of the party if he becomes leader next month, a move Tony Blair repeatedly resisted.

In a statement to the Guardian, Corbyn said he would apologise to the British people for the “deception” in the runup to the 2003 invasion and to the Iraqi people for their subsequent suffering.

Such an apology would be important symbolically – particularly in a party where Iraq remains a sore point, 12 years after Britain joined the US in the invasion – and signal a wider departure from existing Labour’s defence and foreign policy.

Jeremy Corbyn's Iraq war apology will do him good – if not Labour Read more

The MP made a vow that suggests future UK military interventions will become rarer: “Let us say we will never again unnecessarily put our troops under fire and our country’s standing in the world at risk. Let us make it clear that Labour will never make the same mistake again, will never flout the United Nations and international law.”

This effectively rules out Labour under Corbyn from supporting David Cameron’s government in a proposed House of Commons vote to expand to Syria the current UK air strikes in Iraq against Islamic State.

The planned apology over Iraq is aimed at helping win back party members who either left or have stayed but felt estranged as a result of the decision to go to war, which Corbyn voted against. To win in 2020, Labour needed to rebuild its coalition with those who opposed the conflict, Corbyn said.

“So it is past time that Labour apologised to the British people for taking them into the Iraq war on the basis of deception and to the Iraqi people for the suffering we have helped cause. Under our Labour, we will make this apology,” he added.

The Iraq Body Count project puts the civilian death toll at between 143,042 and 162,277 since the invasion that toppled Saddam Hussein, though others put it much higher. The number of British personnel killed in the war was 179 and the US 4,425.

Corbyn’s planned apology attempts to pre-empt the findings of the long-delayed Chilcot inquiry into the Iraq war. “The endless delay on the Chilcot inquiry is wrong. But we don’t have to wait for Chilcot to know that mistakes were made and we need to make amends,” Corbyn said.

Pressure on the six-year-old Chilcot inquiry to produce a report is intensifying. With patience running out, the government may announce next month a fixed timetable, with a date next year finally for publication. The report is expected to be critical of Blair and other senior government figures at the time.

One of Corbyn’s main rivals, Yvette Cooper, who voted for the military action in 2003, also touched on the issue of Iraq on Thursday. When asked on the BBC’s World at One to name one thing the 1997-2010 Labour government did wrong, she replied: “Iraq”. She added: “We need the Chilcot report out to know exactly what happened but we were wrong there were no weapons of mass destruction and also the strategy was wrong because it drew resources from Afghanistan at a crucial stage.”

When asked directly if she personally had been wrong in the way she had voted, she said: “We all were and we have to accept that and take responsibility for that.”

Apologies for historical events such as the one Corbyn is proposing have become increasingly popular over the past two decades, with Blair, Gordon Brown and Cameron making them over issues such as the slave trade, the treatment of the gay second world war codebreaker Alan Turing and the Hillsborough football disaster.

But the Iraq war remains particularly potent. Blair could not bring himself to apologise, issuing only an expression of regret for the loss of life when he gave evidence to the Chilcot inquiry in 2011. The then Labour leader, Ed Miliband, did not apologise either, only describing the war in 2010 as wrong.

The former adviser to president George W Bush, Karl Rove, also refused to apologise in April this when pressed by a US veteran of Iraq.

Corbyn, who opposed the invasion, said in his statement: “As a party, we found ourselves in the regrettable position of being aligned with one of the worst rightwing governments in US history, even as liberal opinion in the US was questioning the headlong descent into war.”

He added that Britain’s relationship with the US would be better in the long term if it were not regarded as likely to follow the White House without question. The Iraq war was wrong in principle, he said, a mistake of horrendous proportions, the price of which is still being paid.

“It has also lost Labour the votes of millions of our natural supporters, who marched and protested against the war. We turned our backs on them and many of them have either withheld their votes from us or felt disillusioned, unenthusiastic and unmotivated,” he said.

Channel 4 News has unearthed footage of Corbyn in 2014 comparing the actions of Isis to US forces retaking the Iraqi city of Fallujah in 2004. “Yes they are brutal, yes some of what they have done is quite appalling, likewise what the Americans did in Fallujah and other places is appalling,” Corbyn told Russia Today.

Corbyn’s campaign, in response, said he regarded Isis as a “vicious, repugnant force that has to be stopped”.

Corbyn is favourite to be elected Labour leader on 12 September. In contrast with his opponents Cooper, Andy Burnham and Liz Kendall, he has been attracting huge audiences at election meetings throughout the country. According to his campaign team, more than 21,000 have attended his rallies, 12,000 people have volunteered to help and more than 7,000 people have donated a total of £166,000 online.

There has been no drop-off in interest. In Nottingham on Thursday night, his campaign team said there was an estimated 900 people in the hall and an overspill of 300 outside. A meeting planned for Cambridge next week attracted more than 1,200 replies for places within hours of being advertised on Thursday.

As part of a major foreign policy overhaul after his election, assuming Corbyn wins, Labour would be unlikely to support the proposed renewal of the ageing Trident nuclear weapons programme; at the general election, the party’s policy was to support it. He is also sceptical about the role of Nato, in particular its eastwards expansion and the standoff with Russia.

Neither the Foreign Office or the Ministry of Defence would comment publicly on domestic political issues, such as the leadership contest. But the US would be opposed to any move by the UK to leave Nato.

A former senior Foreign Office official, who retains close links to his old department, said there was no nervousness at present about the prospect of Corbyn becoming leader, mainly because the expectation is that he is unlikely to become prime minister. But if there was a prospect of him becoming prime minister, it would not go down well either at the Foreign Office or in Washington, he said. “Our relationship with the US would go into deep freeze,” he added.

• This article was amended on 24 August 2015. An earlier version said Iraq Body Count put the civilian death toll since the 2003 invasion at 219,000 . That total is for civilian and combatant deaths.