Retired civil servant John Chilcot, who oversaw the seven-year inquiry, said “the UK chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted. Military action at that time was not a last resort.”

The 2.6-million-word report is an exhaustive verdict on a divisive conflict that – by the time British combat forces left in 2009 – had killed 179 British troops, almost 4,500 American personnel and more than 100,000 Iraqis.

Chilcot said Blair’s government presented an assessment of the threat posed by Saddam Hussein’s weapons with “certainty that was not justified.” He also found military planning for the war and its aftermath were not up to the task.

“The people of Iraq have suffered greatly” because of a military intervention “which went badly wrong,” he said. But he refrained from saying whether the 2003 invasion was legal, and did not find that Blair and his government knowingly misled Parliament or the British public.

Following the release of the report, Blair insisted he had acted in Britain’s “best interests”.

“The report should lay to rest allegations of bad faith, lies or deceit,” he said in a statement issued by his office. “Whether people agree or disagree with my decision to take military action against Saddam Hussein, I took it in good faith and in what I believed to be the best interests of the country.

“The intelligence assessments made at the time of going to war turned out to be wrong. The aftermath turned out to be more hostile, protracted and bloody than ever we imagined. For all of this, I express more sorrow, regret and apology than you will ever know.”

In his decade in office, during which he was elected thrice, Blair oversaw a period of prosperity, secured peace in Northern Ireland and hugely expanded gay rights. But nine years after leaving Downing Street, he remains reviled by many of his countrymen for a conflict that most now consider misguided – and some see as a war crime.

Former British prime minister Tony Blair apologises for ‘wrong intelligence’ before Iraq war and concedes it led to rise of Islamic State

His critics in parliament were already lining up against him ahead of the Chilcot report, examining the possibility of legal action and even a retrospective impeachment.

Last year, he apologised for the wrong intelligence and for some of the mistakes in planning, but said he did not regret removing Saddam Hussein.

The current Labour leadership has broken with Blair’s pro-market policies, but there is no denying the transformation he had on a party that in 1983, when he was first elected to parliament, was in disarray.

Working closely with Gordon Brown, his future finance minister, Blair ditched the party’s commitment to nationalisation of industry and rebranded it as the centrist “New Labour”.

In 1997, he was elected with a landslide, at age 43 becoming Britain’s youngest premier since 1812, and ushered in a new era of hope and confidence for the nation after 18 years of Conservative governments.

The following year brought a peace deal in Northern Ireland, the British province devastated by three decades of violence between Protestant and Catholic communities.

With the economy booming, increases in spending on health and education helped secure another election win in 2001.

After the September 11, 2001 attacks, Blair was quick to ally Britain with US president George W. Bush.

London sent troops to Afghanistan, and in 2003, agreed to join the US-led mission to remove Saddam Hussein in Iraq.

Gaddafi predicted jihadist attacks on Europe, in 2011 phone calls with Tony Blair

But a million people protested on the streets of London against the Iraq invasion, and when the evidence for the war proved flawed, wider dissatisfaction set in.

Blair won the election in 2005, a record third term for a Labour premier but any jubilation was short-lived.

On July 7, 2005, the day after London won the right to host the 2012 Olympic Games, four British suicide bombers attacked the capital’s public transport system, killing 52 people.

Two years later Blair stood down, finally conceding defeat in a long and increasingly bitter power play with Brown, who insisted it was his turn to wear the crown.

Blair has spent most of the last decade abroad, including eight years working part-time as the unpaid envoy for the diplomatic Middle East Quartet, comprising the United Nations, United States, EU and Russia.

His remit was to support the Palestinian economy and institutions in preparation for eventual statehood, but he stepped down last year after failing to produce a meaningful breakthrough.

The controversy over Iraq has not stopped him advocating military action elsewhere, urging Britain and its Western allies to commit ground forces in the fight against Islamic State.

Long-awaited Chilcot report damns British government’s ‘wholly inadequate’ planning for Iraq war

Blair made a rare foray back into British politics to warn of the dangers of leaving the EU in the June 23 referendum – an intervention that fell on deaf ears.

A committed Christian who converted to Roman Catholicism after leaving office, Blair set up a foundation to support interfaith dialogue and counter extremism, and has also worked with governments in developing nations in Africa.

Balancing out his philanthropic endeavours have been a number of lucrative advisory roles, including with the government of Kazakhstan.

His personal income reached tens of millions of pounds, a fact that is also routinely held against him in the British press.