Tony Blair has accepted evidence about Iraq's weapons is now less certain - but still defends taking the UK to war.
Blair says the report shows government "good faith"
Responding to the Butler inquiry, the prime minister said he took personal responsibility for any mistakes made in good faith in the run-up to war.
But having searched his conscience, he was unrepentant about using British troops against Saddam Hussein.
"Iraq, the region, the wider world is a better and safer place without Saddam, Mr Blair told MPs.
In his Commons statement, Mr Blair said Lord Butler's report was the fourth exhaustive inquiry to show the government acted in good faith.
"No one lied, no one made up intelligence. No one inserted things into the dossier against the advice of the intelligence services," he said.
He stressed that Lord Butler had said it would be rash to say weapons will never be found.
"But I have to accept: as the months have passed, it seems increasingly clear that at the time of invasion Saddam did not have stockpiles of chemical or biological weapons ready to deploy," Mr Blair continued.
He accepted evidence of Saddam Hussein's weapons of mass destruction "was indeed less certain, less well-founded than was stated at the time".
"But I cannot go from there to the opposite extreme," he continues, saying Saddam would have started up again as soon as troops left.
Mr Blair said: "For any mistakes made, as the report finds, in good faith, I of course take full responsibility, but I cannot honestly say I believe getting rid of Saddam was a mistake at all."
The prime minister said the Butler report revealed for the first time intelligence about global terrorist groups gathering chemical, biological or nuclear weapons.
After 11 September, no prime minister could responsibly have ignored such a threat.
Mr Blair insisted the government's dossier on Iraqi weapons was not the case for war but for enforcing the will of the United Nations.
He said outgoing MI6 chief Sir Richard Dearlove accepted all Lord Butler's conclusions and would address its recommendations.
Mr Blair added: "I accept the report's conclusions in full.
"Any mistakes should not be laid at the door of our intelligence and security community. They do a tremendous job for our country.
"I accept full personal responsibility for the way the issue was presented and therefore any errors made."
Former Foreign Secretary Robin Cook suggested the unavoidable conclusion of the Butler report was that British troops were sent to war on the back of "false intelligence, overheated analysis and unreliable sources".
But Mr Blair said using force against Saddam Hussein was the right thing to do when Mr Cook was in office in 1998 and was the right thing to do last year.
Tory leader Michael Howard said that the prime minister's credibility had damaged as a result of the way the case was put for war with Iraq.