Speaking in Parliament after Prime Minister's Questions, Jeremy Corbyn paid tribute to the late Cook who "said in a few hundred words what has been confirmed by this report in more than two million".
Cook resigned from the cabinet over the Iraq War in a blistering speech to the Commons in March 2003.
He said: "Ironically, it is only because Iraq's military forces are so weak that we can even contemplate its invasion. Some advocates of conflict claim that Saddam's forces are so weak, so demoralised and so badly equipped that the war will be over in a few days.
"We cannot base our military strategy on the assumption that Saddam is weak and at the same time justify pre-emptive action on the claim that he is a threat.
"Iraq probably has no weapons of mass destruction in the commonly understood sense of the term—namely a credible device capable of being delivered against a strategic city target. It probably still has biological toxins and battlefield chemical munitions, but it has had them since the 1980s when US companies sold Saddam anthrax agents and the then British Government approved chemical and munitions factories.
"Why is it now so urgent that we should take military action to disarm a military capacity that has been there for 20 years, and which we helped to create? Why is it necessary to resort to war this week, while Saddam's ambition to complete his weapons programme is blocked by the presence of UN inspectors?"
Robin Cook died of a heart attack while walking in the Scottish Highlands on 6 August 2005.
The then Liberal Democrat leader, Charles Kennedy, was an implacable opponent of the Iraq war and spoke at the massive anti-war rally in Hyde Park in February 2003 to further voice his resistance to what was by then an almost inevitable conflict.
He was demonised for his stance by many with The Sun even calling him a "spineless reptile".
He said: "International justice also requires a serious restarting of the middle east peace process. I wish the United Nations was able to devote its time and energies to that constructive process rather than the destructive process that we are seeing underway at the moment.
"That absence of a middle east process can only fuel extremism and international terrorism. This is the riskiest moment for Britain since Suez.
"Our country has a principled and a responsible role to play on the world stage but to do so we have to pursue international justice through the United Nations and our government has got to take its people with them. It’s patently failing and that is my message for you today. Thank you.”
Charles Kennedy died last year at his home in Fort William on Monday at the age of 55.