The BBC spent £310,000 on private detectives over six years, according to the corporation's director-general's testimony.
He told the inquiry that investigators were hired 232 times by the BBC between January 2005 and July 2011 – and in one case the BBC used Steve Whittamore, who was later convicted of illegally accessing personal data.
Whittamore was commissioned to find out whether a paedophile had boarded a flight to Heathrow Airport, which Mr Thompson said was "justified in the public interest".
Thompson said that he commissioned a wide-ranging review of the BBC's editorial practices last July, covering phone hacking, "blagging" information, paying police and other public officials for information and the use of private detectives, and found no evidence that any of the corporation's staff had hacked phones or made improper payments to police officers.
He described the ‘Sachsgate’ scandal of 2008, when BBC Radio 2 broadcasted Jonathan Ross and Russell Brand's lewd answering machine messages for Fawlty Towers actor Andrew Sachs, as "a very serious lapse of editorial judgment".
On the issue of media regulation, Thompson said: "Historically the BBC has argued against a statutory foundation, preferring instead the idea of royal charters given over 10-year periods, precisely to stop the risk of political change to its constitution in mid-flight."