The "terrible misadventure" of the Iraq War has seriously undermined Britain's reputation and capacity to act as a force for good, an aid agency report says.
"The Iraq war was a terrible misadventure," Oxfam director Barbara Stocking said. "But it must not cause future prime ministers to return to the caution of the previous Conservative government.
"That administration stood by while the genocides in Bosnia and Rwanda unfolded. We must say 'never again' as much to our failure to stop these atrocities, as to repeating Iraq."
A poll conducted alongside the report found more than two in three voters would still back the use of UK troops as a "last resort to help stop genocide or mass war crimes".
A Foreign Office spokesman said the Government agreed with some of the conclusions of the Oxfam report, "though not all."
He added that the military action in Iraq was justified and denied that the UK now had less influence.
He said: "The UK has pursued an effective foreign policy in the last 10 years, which has been values driven, activist and multilateralist.
"We have rightly focussed on 'hard' security issues such as Iraq, Afghanistan, Bosnia, Kosovo and Sierra Leone as well as 'softer' issues such as climate change and poverty eradication.
"We disagree that the UK now exercises less influence because of Iraq. On the contrary the UK remains at the heart of every major international debate and our influence as consensus builders is recognised worldwide."