On March 17, 2003, Labour MP Robin Cook addressed the House of Commons to announce his resignation as leader of the House. With long-standing rebels Jeremy Corbyn and John McDonnell sitting behind him, Tony Blair’s former foreign secretary denounced the rush toward “military adventure” being pushed by Britain and the United States “without international agreement or domestic support,” drawing both applause and jeers.

It was a crucial starting point in a wave of dissent. While 1.5 million Britons marched in London under slogans like “No blood for oil,” and thirty-six million people protested across the world, opposition was congealing in Parliament. Prominent Conservative fixer John Randall resigned his internal position over opposition to the war, and 121 Labour MPs ended up ignoring Blair’s three-line whip — a serious disciplinary order in Parliament — to oppose military action.

These MPs made for a strange coalition. Beyond the usual suspects of the Socialist Campaign Group were stalwarts of the Labour right like Peter Kilfoyle, while many others had no particular objection to the war but knew that anti-war sentiment in their communities or local Labour branches meant that returning an antiwar vote was a political necessity. Cook’s politics was neither — a long-standing figure of the “soft left” in the ’80s, he was as vigorous a supporter of Michael Foot as he was an opponent of Tony Benn and the left-wing forces that rallied around him.