Tony Blair has defended his decision to go to war in Iraq as a tough choice but one that was "the right thing to do".
Tony Blair said the public must judge if he made the right choices
He told BBC Newsnight's Jeremy Paxman people had to make their own judgement but he took the decision he had to.
"If you want me to apologise for the war in Iraq, I'm afraid I cannot say that I'm sorry we removed Saddam Hussein," the Labour leader said.
During a 30-minute grilling he also said he did not know how many failed asylum seekers there were in the UK.
Despite repeated questioning, he declined to give an estimate.
He said the government's measures on asylum meant the numbers applying were falling, the backlog of cases was lower and more failed asylum seekers were being removed.
"For the very reason that the previous government gave, you cannot determine specifically how many people are here illegally," he said.
"The only long term way of dealing with this issue, however, is to introduce proper controls at borders through an electronic visa regime and identity cards."
He rejected the Tory proposal to set an upper limit on economic migrants as having the potential to cause "tremendous damage" to the economy by denying businesses the workers they needed.
Pressed over the government's use of intelligence in the build-up to the war, Mr Blair insisted the government had been vindicated by four separate inquiries.
He said going to war in Iraq had been a "hard decision" taken for the right reasons.
"You can go through these issues about my integrity, my character, the legal advice... or you can accept that in the end a decision had to be taken.
"There was no middle way, there was no fence to sit on. I took that decision.
"Now I know people strongly disagreed with it. I'm sorry. In the end I had to take the decision as prime minister that I thought was right for the country and I did so."
Asked if he would replace Britain's ageing nuclear deterrent, Mr Blair said he believed it was needed by the country, but said it was a decision for the future.
Tony Blair denied having made a deal with Chancellor Gordon Brown
Questioned on whether Labour would raise taxes, he said the party's spending proposals "are adequately catered for by the tax plans that we've got".
Mr Blair defended the 1% rise in National Insurance during the previous Parliament as necessary for investment in the NHS.
He did not agree with the local income tax proposed by the Lib Dems but did feel council tax should be reformed, he said.
Mr Blair denied having made a deal with Chancellor Gordon Brown to stand down after the election but stressed that they had a "great partnership".
He restated his intention to serve a full third term if re-elected, saying the job of prime minister was still full of challenges.
"I still think we've got things to do. The irony of this job is you are less popular as time goes on but in some ways better equipped to do the job," he said.
"There's masses for me to do and that's what gets you up in the morning."
*Tony Blair will appear on The Paxman Interviews on Wednesday at 1930 BST on BBC One. You can also watch the interviews live by clicking on the election news in video button at the top of all BBC News website election stories.