EDITORIAL USE ONLY : Prime Minister Tony Blair’s reply to the Leader of the House of Commons Robin Cook’ letter of resignation, photographed outside No 10 Downing Street. * Cook tonight quit the Government, saying he could not back war without a fresh United Nations resolution. Mr Cook became the first Cabinet rebel to resign as other senior members of the Government met in Downing Street for an emergency session on the Iraqi crisis. The former Foreign Secretary ended weeks of speculation about his future which intensified when he questioned the legality of military action at last week s Cabinet meeting. Mr Cook was giving a full explanation of his decision to MPs tonight. But he said in a statement: It is 20 years ago that I first joined Labour s shadow cabinet. It is with regret I have today resigned from its Cabinet. I can t accept collective responsibility for the decision to commit Britain now to military action in Iraq without international agreement or domestic support. Resignation letters between Mr Cook and the Prime Minister confirmed he had threatened to go if a new resolution was not passed.