The world will pay for mistakes in Iraq for a generation, Liberal Democrat leader Sir Menzies Campbell has said.
Sir Menzies has always been a vigorous critic of the policy in Iraq
He attacked the lack of planning for an insurgency and the failure to foresee the vacuum that removing Iraqi security forces would create.
"It will take new leadership rather than Bush and Blair to endure the humiliation of seeking regional co-operation," he said.
"Without it the dismemberment of Iraq will remain more likely than not."
He said the UK's relationship with the US should not appear subservient - interests would not always coincide.
Using a keynote speech to mark 100 days of his leadership, Sir Menzies said: "Our relationship with the United States will always be fundamental - but it should be a partnership characterised by candour, honesty and mutual respect.
"Our interests will not always be the same - the relationship should be strong enough to accommodate honest disagreement."
And he warned the chances of Iraq surviving were poor unless there was regional stability brought about by a settlement of the Palestinian/Israeli dispute or "accommodation with Iran".
He said: "Britain and the world will pay for a generation for the mistakes made in Iraq, for the failure to predict, and prepare for, the insurgency that followed; for the failure to fill the vacuum that emerged after disbanding the Iraqi security services; and for the failure to marginalise the aggressors, and enlist the unequivocal support of the majority of Iraqis.
"Sooner or later we shall leave Iraq. But no matter when that may be, Iraq will have a poor chance of survival unless there is regional stability; unless there is a settlement of the Israeli-Palestinian dispute; unless there is an accommodation with Iran.
"The heady talk in US Republican circles of a ripple of democracy through the Middle East has been quietened," he said.
"The State Department is once again more influential than the Pentagon.
"Here at home, apart from the prime minister, no member of the government rushes to defend our presence in Iraq as other than a hazardous necessity."
The Liberal Democrats, under then leader Charles Kennedy, were the only one of the three big UK political parties to oppose the Iraq invasion.