United Nations backing for the Iraq war would have made "life a lot easier", Tony Blair said today.
But the former prime minister said US President George Bush decided the UN Security Council's support "wasn't necessary".
Mr Blair said it was "correct" to say that he shared that view - if Saddam was seen to be continually breaching international laws.
But he stressed he worked on securing a consensus on the war "right up until the last moment".
Lord Goldsmith revealed on Wednesday that he advised Mr Blair in January 2003 that it would be unlawful to attack Iraq without a UN resolution.
It was not until February 27 - less than a month before the invasion began - that the former attorney general finally gave the legal "green light" for military action.
Mr Blair said: "A second resolution was obviously going to make life a lot easier, politically and in every respect."
But he added the US had already decided Saddam would always be "difficult".
"The American view throughout has been, 'This leopard isn't going to change his spots' - he was always going to be difficult," Mr Blair said.
Despite continuing discussion over the threat posed by Iraq at the time, Mr Bush had decided the resolution was not needed.
"His view was that it wasn't necessary but he was prepared to work with one," said Mr Blair.Reuse content