The requirement for clear evidence to justify going to war has just become all the more clear. At a time when the United States claims that Iran is building nuclear weapons capability, but cannot show the world any pictures of missiles or weapons, such evidence is all the more important. No one should be asked to believe such a claim without solid and unambiguous evidence. No one should be asked to accept such claims on good faith alone.

The sad history of lies, false claims and politicians using intelligence to suit their own political aims have become part of the fallout of the Iraq war. George W. Bush knew while the invasion was still happening that his claim of Saddam's weapons of mass destruction (WMDs) was based on forged evidence that Iraq had tried to buy ‘yellow cake' refined uranium from Niger. But now Bush's trail of deception has been hit by yet another revelation.

The Iraqi defector whose claims that Iraq was building biological weapons were crucial to the US case, has admitted that he made up the claims because he wanted the US to go to war and topple Saddam. Rafid Al Janabi was a chemical engineer in the Iraqi military whose detailed descriptions of biological weapons factories, trucks loaded with anthrax, and mobile biological facilities in trains all combined to become a key part of Colin Powell's justification for war.

Unfortunately the claims were not true. "I had a problem with the Saddam regime," Al Janabi told the Guardian this week. "I wanted to get rid of him and now I had this chance." His fabrication achieved his purpose as Saddam was toppled. But the ludicrous failure of intelligence that he created shows how any such future claim has to be treated with great care.