David Cameron says he would not have employed ex-News of the World editor Andy Coulson if he knew what would emerge about phone hacking at the title
The prime minister said that "with hindsight" it appeared the wrong decision and he would offer a "profound apology" if Mr Coulson was found to have lied to him over his involvement.
"You live and learn and believe me I have learnt," the PM said.
However, Labour leader Ed Miliband said there had been a "deliberate attempt to hide the facts".
In an emergency statement to MPs, Mr Cameron also said inquiry into the phone hacking scandal will be widened to examine the conduct of individuals in the police, media and politics.