Miliband blasts 'isolationist' PM
Ed Miliband will accuse David Cameron of pursuing a foreign policy of "small-minded isolationism" that has put party interest first and led to the "biggest loss of influence for our country in a generation".
The Labour leader will also lay part of the blame for the refugee boat tragedies in the Mediterranean at the Prime Minister's door.
But, in the wide-ranging speech at Chatham House, he will also attempt to put some of his own party's ghosts to rest by insisting that he has learned the lessons of the Iraq war.
Mr Miliband will set out the terms for military action under a Labour government and highlight the threats Britain is facing internationally, including from Islamic State, also known as Isil.
In stark contrast to the Conservative promise of an in/out referendum on Britain's membership of the European Union, Mr Miliband will also say he "will never put our national interest at risk by threatening to leave".
The Labour leader will say: "The Tory view threatens to weaken further our position abroad, a pessimistic isolationism that learns the wrong lessons from our past and undermines our nation's future.
"Or a Labour view that says we are stronger as a country when we look boldly, confidently outward to the world, not turning in on ourselves or acting on our own, but working with our allies, never for them: a genuine and hard-headed multilateralism with our values at its core."
Mr Miliband will say that Britain has "more authority when we work" with global allies and will pledge to strengthen the UK's position in international institutions such as the United Nations, Nato, the Commonwealth and the European Union.
The Labour leader will accuse David Cameron of presiding over the "biggest loss of influence for our country in a generation".
"That has happened because the government he led has stepped away from the world, rather than confidently towards it, sidelined in crucial international events time after time under this government, just at the moment when we needed to engage.
"It is time to reject the small-minded isolationism that has characterised this government, diminished the office of prime minister and shrunk the influence of Britain. Because this government's approach has and weakened Britain at a time when the challenges are perhaps greater and more complex than at any time since the Second World War."
The threat from failed states and those stricken by civil war across the Middle East is "spilling over" into Europe through terrorism, illegal immigration and organised crime, he will say.
"The challenge posed by Isil's barbarism is the most pressing case," he will say. "It was right that the UK joined other nations in air strikes against Isil targets in Iraq. But military action alone will not defeat Isil. A long-term multinational political strategy, with regional actors playing a central role, is essential for tackling the rise of extremism across the region and at home.
"And as we do so we must also learn the lessons of previous interventions. These are the vital lessons of our recent past and I will not forget them. Legitimate interventions must be supported by international, regional and local players, carried out with a clearly defined strategy, as well as include a comprehensive transition and post-conflict strategy."
Mr Miliband will say Britain should have done more to plan for the aftermath of the fall of the Gaddafi regime in Libya, which has seen He will say: "Since the action, the failure of post-conflict planning has become obvious. David Cameron was wrong to assume that Libya's political culture and institutions could be left to evolve and transform on their own.
"What we have seen in Libya is that when tensions over power and resource began to emerge, they simply reinforced deep seated ideological and ethnic fault lines in the country, meaning the hopes of the revolutionary uprisings quickly began to unravel.
"The tragedy is that this could have been anticipated. It should have been avoided. And Britain could have played its part in ensuring the international community stood by the people of Libya in practice rather than standing behind the unfounded hopes of potential progress only in principle."
Underlining Labour's pro-European Union approach, he will say Britain's interests are being failed because other leaders "are reluctant to support us because they think we already have one foot out of the door".
He will say: "He has taken us to the edge of European exit because he has been too weak to control his own party and too anxious about the rise of Ukip, a rise he could and should have challenged, but pandered to instead."
"We will rebuild our influence and that starts with the European Union," he will add. "I want a clear message to be sent to our European partners that an incoming Labour government will be serious about leading once again in Europe and serious also about reforming Europe.
"Leaving Europe would be profoundly damaging to the lives or our people and the future of our country. We will never put our national interest at risk by threatening to leave."