The charge:

That Tony Blair, former UK prime minister, in lock-step with US policy, deliberately misled Britain, its parliament and people, into the catastrophe of the illegal invasion of Iraq in March 2003 that resulted in the deaths of at least 100,000 people - a crime against peace and humanity - and in doing so created the circumstances that have brought Iraq to the brink of ruination today.

The defence: Last week, the accused issued a statement in his defence, claiming that the capture of large swathes of Iraq by the Islamic terrorist group Isis - an organisation too extreme for al Qaeda - had nothing to do with the invasion he and then US president George W Bush executed upon the lie that Saddam Hussein possessed weapons of mass destruction (WMD) that threatened the West. Blair said: "We have to liberate ourselves from the notion that 'we' have caused this. We haven't."

Exhibit A: Rebuilding America's Defences, the founding document of The Project for the New American Century (PNAC) . The PNAC was effectively the Bush cabinet-in-waiting prior to the 2000 election. It included Dick Cheney, who went on to become vice-president; Donald Rumsfeld, defence secretary; Bush's brother, Jeb; Lewis Libby, Cheney's chief of staff; Paul Wolfowitz, Rumsfeld's deputy; and other key members of the Bush administration. This was the "brain" of the neo-conservative movement hell-bent on regime change in Iraq. Blair was fully signed up to the neo-con vision, their ideology providing a key motive for the crime in question.

Rebuilding America's Defences was the foundation for the Bush-Blair doctrine of pre-emption. Written in September 2000, just months before the Bush election, it said: "The United States has for decades fought to play a more permanent role in Gulf regional security. While the unresolved conflict with Iraq provides the immediate justification, the need for a substantial American force presence in the Gulf transcends the issue of the regime of Saddam Hussein."

In other words, even if Saddam were removed from power, America would still want troops in the Gulf. Rebuilding America's Defences talks of "a blueprint for maintaining global US pre-eminence" and a "Pax Americana", which would require the US and its allies to "fight and decisively win multiple, simultaneous major theatre wars as a 'core mission'."

Exhibit B: The receipts from Iraq for the sale of weapons of mass destruction from Britain and America. Details of sales of WMD to Saddam up to 1989 are contained in a Senate report into US exports, called the Riegle Report. Saddam is known to have used WMD in 1988 against the Kurds - in the town of Halabja, up to 5,000 were gassed. The attack took place when Saddam was engaged in the Iran-Iraq war against Ayatollah Khomeini and was, in the language of US-UK diplomacy, "a son of a bitch, but our son of a bitch". This was prior to the first Gulf War in 1990 when Saddam invaded Kuwait, seized its oil and became the West's enemy.

However, the Riegle Report shows America sold Saddam the following germ warfare capabilities: anthrax; botulism; histoplasma capsulatuma, a germ similar to TB; and clostridium perfringens, which causes gas gangrene. Some 16 UK companies also sold weaponry to Saddam.

The West was aware Saddam had begun a series of banned weapons programmes in the 1980s. In December 1983, Donald Rumsfeld, then president Ronald Reagan's special envoy to the Middle East, met Saddam, shook his hand and discussed the curtailment of Iran. A 1984 US state department memo shows America knew it was selling "dual use" technology to Iraq - material that could be used for civilian purposes or to create nuclear, biological or chemical weapons. The CIA estimates Iran took more than 50,000 casualties from Iraqi chemical weapons. British politicians were equally aware.

Exhibit C: Statements from key UN weapons inspectors. Scott Ritter was the United Nations' former chief weapons inspector in Iraq, a former US Marine intelligence officer and a Republican who voted for Bush, as well as being a Gulf War veteran. Ritter told me in 2003 he knew "categorically" that weapons inspections imposed on Saddam in the wake of his defeat in the first Gulf War destroyed 90% to 95% of Iraq's WMD stockpiles - built up with British and American material. The remaining stockpiles were unusable by 2003. Ritter was clear that any invasion of Iraq on the grounds of WMD capabilities would be based on lies. Hans von Sponek, the UN's former co-ordinator in Iraq and UN under-secretary general, also told me he had visited alleged chemical and biological weapons sites as recently as September 2002 and found them "comprehensively trashed". Dennis Halliday, former UN assistant general-secretary and UN humanitarian co-ordinator in Iraq, told me that at least one million Iraqis died as a result of sanctions imposed to remove WMD from Saddam: WMD that the world's experts in WMD said no longer existed.

Exhibit D: Strategic Energy Policy Challenges For The 21st Century. This paper, prepared for Dick Cheney, helped the Bush cabinet agree before September 11, 2001 that Iraq was a risk to world oil markets and therefore a risk to America. It has been said this may point to the true motive for invading Iraq.

The document stated that "the United States remains a prisoner of its energy dilemma" and "Iraq remains a destabilising influence … to the flow of oil to international markets from the Middle East … Saddam Hussein has also demonstrated a willingness to threaten to use the oil weapon and to use his own export programme to manipulate oil markets". As a result, the US "should conduct an

immediate policy review toward Iraq, including military, energy, economic and political/diplomatic assessments".

Exhibit E: Operation Rockingham, a British spying operation established by the Defence Intelligence Staff within the Ministry of Defence in 1991. Scott Ritter knew members of Rockingham and said the spying outfit was "dangerous" and authorised at "the very highest levels". He added: "Rockingham was spinning reports, and emphasising reports that showed non-compliance [by Iraq with UN inspections] and quashing those reports which showed compliance. It was cherry-picking." It became "part of an effort to maintain a public mindset that Iraq was not in compliance … They had to sustain the allegation that Iraq had weapons of mass destruction, even though [UN inspections were] showing the opposite.

"Rockingham received hard data but had a pre-ordained outcome in mind. It only put forward a small percentage of the facts when most were ambiguous or noted no WMD."

Dr David Kelly - the British weapons expert who took his own life after being exposed as the source behind a BBC claim that the Blair government had "sexed up" a dossier claiming Iraq had WMD - worked with Rockingham. Ritter said Kelly was the "go-to person" for translating the often confusing data from weapons inspections "into concise reporting that could be forwarded to analysts in the British intelligence community as well as political decision-makers". Ritter added that, thanks to Rockingham, "there existed a seamless flow of data from Iraq, though New York to London, carefully shaped from beginning to end by people working not for the UN Security Council but for the British government. Iraq's guilt, pre-ordained by the government, became a self-fulfilling prophecy."

Exhibit F: The Office of Special Plans (OSP). In effect, this was America's version of the Rockingham cell. It was set up when the Iraq desk of the Near East and South Asia affairs (NESA) office in the Pentagon was transformed into the OSP. Lieutenant Colonel Karen Kwiatkowski worked inside NESA up to the outbreak of the war. "At the OSP," she told me, "what they were doing was looking at all the intelligence they could find on WMD."

She added: "That was the focal point, picking bits and pieces that were the most inflammatory, removing any context that might have been provided in the original intelligence report, that would have caused you to have some pause in believing it.

"They would take items that had occurred many years ago and put them in the present tense … The other thing they would do would be to take unrelated events that were reported in totally unrelated ways and make connections that the intelligence community had not made."

One story that made the British papers shortly before the invasion claimed Saddam had a team of beautiful female assassins in deep cover in the UK as sleeper agents, posing as belly dancers. This myth has been connected to the work of Rockingham and the OSP. OSP intelligence was the kind of bogus material also used to support erroneous claims presented to the world that secular Saddam was working with the religious fundamentalists of al Qaeda.

Exhibit G: Dodgy dossiers. The Joint ­Intelligence Committee under the chairmanship of MI6's John Scarlett was meant to have full control over the contents of dossiers outlining Iraqi WMD - in effect, Blair's case for war. However, it became fully politicised. A special adviser to Alastair Campbell, Blair's spin doctor, wrote of one early draft: "Very long way to go … Think we're in a lot of trouble with this as it stands now." Campbell later admitted he was involved from a "presentational point of view".

Here's how the most contentious claim was handled in draft form: "Chemical and biological munitions could be … ready for firing within 45 minutes." This claim was already based on cherry-picked OSP/Rockingham reports, but when it was published it had become much more firm - the key section now read that the warheads "are deployable within 45 minutes". Campbell told Scarlett - who he described as his "mate" - that there were weak passages in the draft. Scarlett wrote back: "We have been able to amend the text in most cases as you proposed."

Tony Blair eventually wrote in a final dossier foreword: "The assessed intelligence has established beyond doubt that Saddam Hussein has continued to produce chemical and biological weapons." The case for war was made, put to Parliament and voted for overwhelmingly.

Exhibit H: Copious warnings from within ­British intelligence against any invasion of Iraq. Intelligence sources confirmed to me that many spies had been openly sceptical about WMD in Iraq for years. They concurred with the notion of cherry-picking and pressure to find evidence against Saddam. This newspaper published these allegations on our front page at the time. In a July 2002 secret Downing Street memo, it is noted that Bush wants to "remove Saddam through military action, justified by the conjunction of terrorism and WMD. But the intelligence and facts were being fixed around the policy." In January 2004, David Kay, the CIA-appointed head of the Iraq Survey Group with the task of finding Saddam's WMD, resigned, saying there were no stockpiles.

Exhibit I: Intelligence leaks confirming Blair was warned the invasion would lead to chaos in Iraq and terrorism on the streets of Britain. One report from the Defence Academy, an MoD think tank, written by a naval commander, said: "The war in Iraq … has acted as a recruiting sergeant for extremists across the Muslim world … al Qaeda ideology has taken root within the Muslim world and Muslim populations within Western countries. Iraq has served to radicalise … disillusioned youth and al Qaeda has given them the will, intent, purpose and ideology etc."

In the US, a declassified National Intelligence Estimate found that the "Iraq conflict has become the cause celebre for jihadists … cultivating supporters of the global jihad movement."

Exhibit J: The launch of the war. Blair ­committed himself to waging war against Iraq whether or not the UN supported military action. In the end, no UN support was forthcoming. In 2002, inter-departmental advice for UK Government ministers stated that the objectives towards Iraq were "the reintegration of a law-abiding Iraq, which does not possess WMD … into the international community. Implicitly, this cannot occur with Saddam in power … the use of overriding force in a ground campaign is the only option that we can be confident will remove Saddam."

Later in 2002, Blair met Bush in Crawford, Texas, where they discussed the "need for effective presentational activity". The die was cast. War was coming. Former UN secretary-general Kofi Annan later said the invasion was "illegal".

Exhibit K: The conduct of the Iraq War. ­Western business followed US-UK forces into Iraq, ­carving up the nation and profiteering from war. The policy was one of exploitation, not nation-­building. British and American troops were allowed to behave appallingly - from the atrocities of Abu Ghraib to the detention, torture and even death of Iraqi civilians at the hands of British soldiers. One corporal, Donald Payne, remains the only British soldier to be convicted of a war crime following the death of an Iraqi citizen who was hooded and beaten - he was found to have 93 injuries on his body.

The occupation brought chaos to Iraq. Al Qaeda moved in to a country where it had not been before, and laid down deep roots. As far back as August 2003, al Qaeda in Iraq blew up the UN HQ in Baghdad. Soon its leader, Abu Musab al-Zaraqwi, had the nation in the grip of fear, and sprung to international attention with the televised beheadings of captives including Nick Berg and Ken Bigley.

The behaviour of allied troops further alienated the population, with horrors such as the wedding party massacre at the town of Makaradeeb in which 42 civilians, including 13 children, were killed. Al Qaeda, made up of Sunni Muslim extremists, used the chaos to bring terror to the Iraqi Shia Muslims they hated.

Shrines were bombed, holy days targeted. The predominantly Shia armed forces and government replied with death squads and extra-judicial executions against often innocent Sunnis. Torture became routine. Bodies were found with acid burns and drill marks and still wearing police handcuffs. Divisions deepened.

The country split along ethno-religious lines. Over the border in Syria - a country some believe might have remained at peace without the seismic shock of the invasion of Iraq - the ­fundamentalist and brutal Isis movement saw its chance and began making inroads within Iraq's borders. Town after town fell. Fallujah, Samarra, Mosul, Tikrit. Isis now threatens Baghdad.

Verdict: Guilty.

Neither Blair nor Bush will ever face punishment for taking the US and UK into an illegal war they knew was based on lies, and killing countless innocent people. Western statesmen do not end up in The Hague facing war crimes charges. The punishment is on us and the Iraqi people.

The standing of Britain has been degraded abroad, trust in politics destroyed at home. Our morality is so drained that the very concept of military intervention to save Iraq from Isis is rendered absurd. We brought that nation to ruin and now we watch as it falls, with echoes of the Khmer Rouge taking Cambodia back to Year Zero. Where there was no terrorism, we created a terrorist homeland.

Chief among Blair's crimes is that while he may have blood on his hands, he has spread the blood on to us, because in a democracy we must carry some of the blame for our elected leaders, even if they try to blind us to the truth through a web of deceit, chicanery, bullying and sin.

Neil Mackay is the Sunday Herald's Head of News.

He is the author of The War On Truth, which investigated the roots of the invasion of Iraq; and of the novel All The Little Guns Went Bang Bang Bang