LONDON: Former Prime Minister Tony Blair acknowledged on Friday that Saddam Hussein didn't become a bigger threat after September 11, but said his perception of the risk posed by terrorists acquiring weapons of mass destruction was dramatically changed by the attacks. Blair told Britain's Iraq Inquiry that his contentious decision to back the 2003 US-led invasion of Iraq was inspired by fears of another, even deadlier, terror attack. 'It wasn't that objectively he (Saddam) had done more, it was that our perception of the risk had shifted,' Blair said. 'If those people inspired by this religious fanaticism could have killed 30,000, they would have. From that moment Iran, Libya, North Korea, Iraq ... all of this had to be brought to an end. 'The primary consideration for me was to send an absolutely powerful, clear and unremitting message that after September 11 if you were a regime engaged in WMD (weapons of mass destruction), you had to stop.' Clutching a sheath of documents, a tense-looking Blair sat down in a London conference centre to answer questions from the Iraq Inquiry, a wide-ranging investigation commissioned by the government to scrutinise the behind-the-scenes machinations from 2001 through Britain's decision to join the costly and unpopular Iraq war. Blair was questioned about charges that his government was so determined to topple the Iraqi dictator that they exaggerated the content of intelligence reports on Iraq's supposed weapons of mass destruction. He was pressed on when exactly he offered US President George W Bush support for an invasion. The former British ambassador to Washington, Christopher Meyer, has said it appeared that an agreement was 'signed in blood' by Bush and Blair at the president's ranch in Crawford, Texas, in April 2002. 'The only commitment I gave (at Crawford) was a commitment to deal with Saddam,' Blair said. He said he told Bush 'we will be with them in dealing with this threat.' Blair said other world leaders did not feel the same way he and Bush did. 'Although the American mindset had changed dramatically (after September 11) - and frankly mine had as well - when I talked to other leaders, particularly in Europe, I didn't get the same impression.' An audience gathered in a central London convention centre for the session included family members of soldiers and civilians killed or missing in Iraq. Commuters arriving at the Westminster underground station near the hearing centre were met by several people gathering signatures for a petition urging that Blair be tried as a war criminal. Blair had arrived shortly before 0700GMT (0200EST) today, dodging demonstrators by entering the conference centre through a cordoned-off rear entrance. About 150 protesters clustered outside shouted slogans including 'Jail Tony' and 'Blair lied - thousands died,' as rows of police officers looked on. As Blair testified, demonstrators outside the convention hall read aloud the names of civilians and military personnel killed in Iraq.