Was the invasion of Iraq justified?

The original recommendation to Blair was that toppling an evil dictator just because he's an evil dictator was a violation of International Law and that he shouldn't do it, further, we now know that Blair was informed 10 days before the invasion that Saddam's WMDs had already been dismantled. He ordered the troops in anyway because he'd promised Bush that Britain would back anything he did no questions asked before finding out what Bush intended to do. It was also known that Saddam had almost certainly had nothing to do with the 9/11 attack on New York which Bush had used to justify the invasion of Afghanistan. Given that Saddam posed no threat to Britain or it's allies I would say the invasion was totally unjustified, and illegal as well.