How many of those calling for Putin’s arrest were complicit in the illegal invasion of Iraq?

It goes beyond hypocrisy. It’s an assault on memory. Gordon Brown, calling for a special tribunal to punish the Russian government, correctly states that an act of aggression – invading another nation – was identified by the Nuremberg tribunal as “the supreme international crime”. It is, he wrote in the Guardian, not just Vladimir Putin who should be prosecuted, but also his “henchmen”. These include members of the Russian and perhaps Belarusian national security councils, and a range of political and military leaders. All should be held to account for this “manifestly illegal war”, he wrote on his website.

Condoleezza Rice, who was George W Bush’s national security adviser, was asked of Russia’s aggression on Fox News, “when you invade a sovereign nation, that is a war crime?” She replied: “It is certainly against every principle of international law and international order.”

Brown and Rice are right about Russia. Its government, in invading Ukraine, has clearly committed the crime of aggression, a crime in which, as Brown points out, its senior officials are complicit. The same applies to the US and UK governments, which invaded Iraq 20 years ago today. Among the most senior perpetrators were Rice and Brown.

The seventh of the Nuremberg Principles, which Brown cites in calling for Russian prosecutions, points out that “complicity” in a war of aggression “is a crime under international law”. Both officials would clearly qualify as complicit. Rice was one of the architects of the war. Brown, as a cabinet member, was party to the decision. As chancellor of the exchequer, he financed the war.

Related: Abuses and intelligence failures hang over UK 20 years after Iraq war

No one can credibly deny that the invasion of Iraq met the Nuremberg definition. The Chilcot inquiry, whose terms were set by Brown when he was prime minister, was forbidden to pronounce on the legality of the war. But it concluded that “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.” In other words, it failed to meet the UN charter’s criteria for legal warfare. The former law lord, Lord Steyn, came to the same conclusion: “In the absence of a second UN resolution authorising invasion, it was illegal”. The former lord chief justice, Lord Bingham, called the Iraq war “a serious violation of international law”. A Dutch inquiry, led by a former supreme court judge, found that the invasion had “no sound mandate in international law”.

The attackers went out of their way to eliminate peaceful alternatives. Saddam Hussein desperately sought to negotiate, eventually offering everything the US and UK governments said they wanted, but they slapped his hand away, then lied to us about it. When the UN sought diplomatic solutions, US officials went into what they called “thwart mode”, sabotaging negotiations.

When the head of the Organisation for the Prohibition of Chemical Weapons, José Bustani, offered to resolve the impasse over weapons inspections in Iraq, the US government illegally ousted him. The first government to support his sacking was the United Kingdom’s.

The government in which Brown was chancellor was repeatedly warned that its planned invasion would be illegal. A year before the war, the then foreign secretary, Jack Straw, explained that for a war to be legal, “i) There must be an armed attack upon a State or such an attack must be imminent; ii) The use of force must be necessary and other means to reverse/avert the attack must be unavailable; iii) The acts in self-defence must be proportionate and strictly confined to the object of stopping the attack”. None of these conditions applied. The Foreign Office, according to its deputy legal adviser, Elizabeth Wilmshurst, consistently counselled that an invasion would be unlawful without a new UN resolution. She explained that “an unlawful use of force on such a scale amounts to the crime of aggression”. A Cabinet Office memo warned: “A legal justification for invasion would be needed. Subject to Law Officers’ advice, none currently exists.”

As for “law officers’ advice”, the then attorney general, Lord Goldsmith, warned that there were only three ways in which an invasion could be legally justified. They were “self-defence, humanitarian intervention, or UNSC [UN security council] authorisation. The first and second could not be the base in this case.” The government failed to obtain UN security council authorisation. At the Chilcot inquiry, Lord Goldsmith testified that, after he gave advice Tony Blair didn’t want to hear, the prime minister stopped asking. Just before the war, though the facts had not changed, Goldsmith changed his mind.

There is another way of saying “crime of aggression”: an act of mass murder. The invasion of Iraq killed hundreds of thousands of people. We cannot be more precise than that, as the invading forces refused to measure the carnage. But it is almost certainly the greatest crime against humanity so far this century. Blair, Brown, Bush and Rice are as guilty of a “manifestly illegal war” as Putin and his close advisers.

Related: The Guardian view on Iraq, 20 years on: the costs of war | Editorial

But who gets prosecuted is a matter of victors’ justice. For example, until it issued a warrant last week on another charge for the arrest of Putin and one of his officials, there had been 31 cases brought before the international criminal court. Every one of the defendants in these cases is African. Is this because Africa is the only continent where crimes against humanity had occurred? No. It’s because Africans accused of such crimes do not enjoy the political protections afforded to the western leaders who perpetrate even greater atrocities.

Instead of facing justice, the killers walk among us, respected, revered, treated as the elder statesmen to whom media and governments turn for counsel. Brown can pose as an august humanitarian. Alastair Campbell, who oversaw the compilation of the “dodgy dossier”, which provided a false case for war, and is therefore as complicit as any of Putin’s “henchmen”, has been thoroughly screenwashed: in other words, rehabilitated, like other grim political figures, by television. He is now treated as a kind of national agony uncle.

There has been no reckoning and nor will there be. This greatest of crimes has been so thoroughly airbrushed that its perpetrators can anoint themselves the avenging angels of other people’s atrocities. To quote King Lear: “Plate sin with gold, and the strong lance of justice hurtless breaks: arm it in rags, a pigmy’s straw does pierce it.”

• George Monbiot is a Guardian columnist