Steve Richards: Progressive causes everywhere will feel the loss of an indispensable politician

Who do we turn to now for a vividly insightful running commentary on the consequences of the war?

In the current mood of febrile introspection on the centre-left, Cook had a pivotal role as an advocate of a visionary, robust alternative to Tony Blair's narrow pragmatism and as a figure with close ties to progressives in other parties in Britain and in Europe. He mattered more now than at any point in his political career.

Since his death, parts of his famous ministerial resignation speech have been replayed on the news bulletins. The words were mesmerising as they were delivered on the eve of the war against Iraq, but - unlike many speeches that intoxicate fleetingly - this one sounded even better now. Never before has a departing minister been more grimly vindicated by events.

Cook warned in the speech that there were no weapons of mass destruction in Iraq and that the war would lead to the fracturing of the international coalition that had built up after 11 September. A few of his cabinet colleagues also recognised that Blair was getting dangerously out his depth in his desperate manoeuvrings. Only Cook had the courage to resign, acquiring an even more important and powerful voice as a result.

Who do we turn to now for a vividly insightful running commentary on the consequences of the war? Cook provided a public service at a time when ministers conspired to keep Iraq off the agenda and pretended that the war was not a factor in making London a more potent target for terrorists.

Cook also became the most powerful pro-European voice in British politics. We will not hear him again on Europe at a time when the Government has retreated into a timidly Euro-sceptic comfort zone in which its message echoes previous Conservative administrations: We will be pro-European as long as Europe follows us. Cook was subtler than that, more aware of the damage caused by the war in terms of Britain's relations with other EU countries. He knew, too, the importance of projecting a more positive case in Britain instead of relying on the defensively counter-productive argument that Europe will be tolerable once we have imposed our will on what it does.

Cook's belated conversion to Europe was part of a wider rethink about Britain and its place in the world. In the mid 1990s, he worked closely with senior Labour colleagues and some Liberal Democrats on a package of reforms, including devolution, reform of the House of Lords and a proposed referendum on electoral reform. He carried out the project with the active encouragement of Blair, but unlike his leader he viewed the exercise as more than artful political repositioning. He believed in the substance of the package. I often joked with him that, on these matters at least, he was far more Blairite than Blair.

The last time I saw him was at a recent meeting organised by The Independent on electoral reform. He delivered an electrifying speech and even managed to get some laughs, a sparkling achievement on such a dry issue. Have you heard the one on the Single Transferable Vote? I was reminded at the meeting that Cook was a great orator capable of holding an audience on any subject. There are few in the Labour party who possess such skill. The party conference this autumn and in succeeding years will be much duller without Cook lighting up a score of fringe meetings.

In the coming years he would have been more than a sparkling communicator. Cook was uniquely well-placed to help forge the progressive consensus that Gordon Brown seeks to bring about. In his support for Europe, improved and equitable public services, opposition to the war and the need to regain political trust partly by introducing sweeping constitutional reform, he was the epitome of a progressive in early 21st century Britain.

Equally important, he had more than made up with Gordon Brown after decades when they could not stand each other. Over the last year, Cook and Brown met regularly for a cup of tea. Sometimes the conversations took place in Cook's office at Westminster. Occasionally Cook popped into the Treasury. The main theme of their talks was the need for a more firmly entrenched progressive consensus, rebuilding politics after the nervy, triangulated and media-obsessed leadership of Blair.

These politically intimate conversations were an astonishing twist after their long lasting feud. In the early 1990s Frank Dobson, who was a friend of both men, suggested to John Smith that he took them out to dinner. Smith replied to Dobson that it would be a complete waste of time as the relationship of the two men was beyond repair. Confident of his mediating skills, Dobson still arranged the dinner. A few minutes after the dinner ended, earlier than planned, a pale and exhausted Dobson staggered into Smith's office and said: "You're right. They hate each other." But in recent years they came instead to respect each other. Cook said publicly that Brown should become Prime Minister. I am certain Brown would have brought him back to the cabinet in a senior role.

I have read over the last day or so that Cook was most content playing a leading role in the "awkward squad" at Westminster. This is not the case. By instinct he was a loyalist, supportive of Neil Kinnock's reforms, even when he had some private doubts, and backing John Smith's successful leadership bid in 1992. Even when he had worries about the direction of policy under Blair, he was largely loyal.

He was not a natural rebel, which is why it took the monstrous enormity of Iraq to provoke his resignation. During the election he showed the degree of his loyalty by campaigning in constituencies with large Muslim populations, urging them to support Blair in spite of the war. The continuing prominence of Cook made Labour more acceptable to an army of disillusioned supporters.

When I recently had a coffee in Cook's Westminster office he had to pop out to vote in a division. For ten minutes I looked at the messages in the hundreds of cards on his shelves and walls. They came from celebrities such as the actress Emma Thompson and ordinary voters, all of them thanking him for the stand he took on the war. Who have Emma Thompson, the Muslim constituencies and others got to speak for them now? Most politicians are dispensable - Cook was not. We needed him, and as lesser politicians address the challenges of the years ahead they will curse the premature silencing of a truly progressive voice.

s.richards@independent.co.uk