A British military helicopter ran out of fuel, allowing Osama bin Laden's Iraqi commander to evade capture for further 15 months, the Guardian reported on Sunday after studying the Iraq war documents released by WikiLeaks.
The astonishing blunder in March 2005 gave Abu Musab al-Zarqawi a Jordanian associate of bin Laden with a $25 million reward on his head an extra 15 months to expand Al Qaeda operations in Iraq, bringing the country close to a civil war.
The paper said, according to the military intelligence files, British troops came close to capturing their most wanted target in Iraq. But the operation collapsed after the only surveillance helicopter monitoring him ran out of fuel and had to return to base.
His fundamentalist Sunni supporters were behind some of the worst atrocities aimed at Iraq's Shia majority population as well as countless attacks on US and Iraqi government forces.
Their bombing of a sacred golden-domed Shia shrine in Samarra in February 2006 led to a wave of revenge killings that lasted for a year and a half, the report said.
Zarqawi was eventually located by the Americans in a house north of Baghdad in June 2006 and killed with his family by a US air strike.
The British near-miss was hugely expensive.
Zarqawi had first come to international attention when his gunmen kidnapped Ken Bigley, a British contractor working on reconstruction projects, and two American colleagues in Baghdad in September 2004.
They were shown on their knees in videos and beheaded two days later after the authorities refused to negotiate their release.
This was a minor atrocity compared to what Al Qaida was to do in Iraq in 2005 and 2006, the report said.