The British attorney general has circulated legal advice to the prime minister's office, Foreign Office and Defense Ministry warning that a preemptive military strike on Iran could violate international law, the Guardian's Nick Hopkins reports. The existence of this secret document suggests that the U.K. government believes that Iran does not currently meet the legal threshold for a "clear and present danger" that would merit such an attack.

Though Iran's illegal uranium enrichment is moving it closer to the capability to assemble a nuclear weapon, U.S. intelligence agencies do not believe that Tehran has affirmatively decided to build a bomb. The British legal memo would seem to underscore this view, as well as raise the question of whether Iran would have to cross that line for a military strike to meet the requirements of international law.

The Guardian also reveals that the U.K. is using this legal document to deny the U.S. assistance in contingency planning for a strike on Iran. The U.S. is reportedly asking for access to British airbases that are strategically located on remote islands.

The bases aside, the apparently staunch U.K. opposition to working with the U.S. on this is striking, particularly after British Prime Minister Tony Blair so closely joined U.S. President George W. Bush in planning and executing the wars in Afghanistan and Iraq. The 2003 Iraq invasion became a source of considerable political backlash in the U.K., including a two-year official investigation that culminated in Blair being summoned to a bruising public inquiry.

Based on this story, it appears that the U.K. wants little or nothing to do with even U.S. planning for a potential strike on Iran, much less the attack itself. "I think the U.S. has been surprised that ministers have been reluctant to provide assurances about this kind of upfront assistance," an anonymous British source told the Guardian, speculating that this meant Washington might not even inform London of an attack until after it had happened. "In some respects, the U.K. government would prefer it that way."