Today's papers react to yesterday's dramatic developments.

Times

The Parliamentary Labour Party cannot afford to behave as if it were a debating society shorn of responsibility. It should recognise that Mr Blair has, as he was urged by many MPs to do, fought as hard as possible to obtain another resolution but found himself blocked by a right-wing French president motivated more by reckless opportunism than affection for the UN Charter. They should acknowledge that Mr Blair's efforts deferred a military conflict for a number of months, and that he has exercised a positive influence on the United States. Britain, and perhaps Ms Short, will have a crucial role in the rebuilding of Iraq and in the newly unfolding Middle East peace process. The exercise of power is not painless. Protesting from the fringe, shunning the realities of politics, standing back from conflict, is often far more comforting. Much of the history of the Labour Party has been that of an allergy to awkward choices and a preference for the warm irrelevance of marches and petitions. Mr Blair had hoped that four successive general election defeats would rid his colleagues of this collective affliction. The novelty of new Labour, his invention, was to be a willingness to deal with Britain and the world as it is, not how some may want it to be. He will discover tonight how many of his colleagues have yet to rise to the challenge of reality.

Telegraph

"Those voting in parliament today need to consider what sort of a nation Britain is. Ours is the only European country in the post-war era which has never shirked its obligation to try to preserve peace in the world and defend the interests of the West against its enemies. This fact has maintained our high military reputation, our global influence and our self-esteem. From 1940 to the present day, we have continuously recognised that we must be strenuous for peace and freedom, and that this sometimes means fighting for them. In this, we have sustained with the United States the most important alliance of modern times. If we slink away now, we will suffer much more than the relatively minor catastrophe of losing a prime minister: we will be weak and friendless, and we ought to be ashamed.

FT

MPs must balance their moral conscience about the war against the long term interests of their constituents and their party. Mr Cook was dignified in departure yesterday, citing his inability to accept collective responsibility for the decision to commit Britain to military action without international agreement or domestic support; he is a loss. Other MPs will feel the need to register their opposition to a unilateral war that carries grave implications for the UN, the European Union, Nato and the entire multilateral framework. It would be more than a pity nonetheless, if the revolt were of such a scale as to sweep away a prime minister who still has much to offer his country.

Guardian

The model clarity of Mr Cook's behaviour yesterday contrasts with the way that Clare Short has responded to the government's crossing of the Rubicon. A week ago, Ms Short delivered a sweeping indictment of government policy on Iraq, pledging to quit if there was no second resolution at the UN. Yesterday, when the second resolution was abandoned, Ms Short seemed to have second thoughts. Perhaps, by her earlier challenge, Ms Short managed to win key concessions on post-war reconstruction. If so, she has played hardball, and won. But she should not imagine that the public will be at all impressed. It is hard to believe that Ms Short's reputation for principle will recover if she now decides not to follow Mr Cook out of the cabinet door.

Independent

It is a strange paradox that while Mr Blair's arguments have failed to convince, his patent sincerity has impressed, banishing his reputation as a fickle politician without convictions. His address and answers after Sunday's Azores summit were worthy of a first-class statesman, leaving Mr Bush looking like an ill-informed amateur. Key elements of his foreign policy, however, are in shreds. Any ambition he might have had to lead Europe in the future is at an end. Britain's reputation and influence in the Arab world cannot but be diminished. Britain risks being seen once again as Washington's junior partner and no more. The next 24 hours will show how profoundly the kaleidoscope to which Mr Blair referred 18 months ago has been shaken; how many of the myriad shards are in flux and how long they may take to settle. We fear that it could be a very long time.

Mail

Yes, the prime minister will certainly face serious political consequences if this campaign goes badly. But consider what the national mood will be if the victory is swift, if - God willing - the casualties on both sides are kept to a minimum, if the horrors of Saddam's jails and torture chambers are exposed, if his weapons of mass destruction are displayed for all to see and if the Iraqi people celebrate their liberation from years of tyranny. Of course there are a great many 'ifs'. But this is the outcome Mr Blair believes in passionately, the outcome he has risked everything to achieve. The whole country will pray he is right. Should that prove to be the case, his political position will, deservedly, be unassailable.

Sun

In today's debate, Blair clearly faces a momentous challenge to his authority. Cook may be a pipsqueak by comparison, but like a small dog he packs a nasty bite. At least Blair has him out in the open where he can deal with him. Ex-foreign secretary Cook was scathing about Israel, the only democracy in the Middle East, and about president Bush. And his claim that if Al Gore had been elected president, we would not be on the brink of war, was a vicious insult. Americans will be amazed by the views held by a former member of Blair's government. They will watch on TV news as Cook gets a standing ovation from fellow MPs and wonder if - with our troops poised to attack in the desert - Britain has gone mad. The question now is how long Clare Short can continue in office. Like Cook, she is the enemy, too - but she is the enemy within.

Express

With the nation on the brink of war prime minister Tony Blair needs every ounce of support from Parliament, his cabinet and his people. Our troops must know that the whole nation is behind them. We understand the deep concerns of those who recoil from going to war without a second resolution but the world cannot stand by while Saddam Hussein grows stronger on the weakness of others. The resignation of Robin Cook was entirely predictable and he will be little missed...Now the spotlight turns to the volatile Clare Short. Ms Short has always claimed to be a woman of principles but they now see to be deserting her. How can she have the gall to stay in the Cabinet after calling her leader reckless and threatening to resign if we go to war without a resolution. She should go. Mr Blair needs people he can count on.

Mirror

Tony Blair has received many plaudits for his courage in having conviction and sticking to it. We keep hearing what a bold leader he has been, working tirelessly to get the Americans to the United Nations negotiating table and striving valiantly to secure a further resolution. But the truth is he has failed. And the real act of courage would be if he rang George Bush this morning and told him that he could not, under these circumstances, go to war.