The BBC spent £310,000 on private detectives over a six-year period, the Leveson Inquiry heard today.
The corporation once used investigator Steve Whittamore, who was later convicted of illegally accessing personal data, to check whether someone was on a particular flight.
On another occasion a BBC journalist commissioned a private detective to find out the owner of a car from its number plate, the hearing was told.
BBC director-general Mark Thompson told the press standards inquiry that the corporation's staff used investigators 232 times between January 2005 and July 2011 at a total cost of £310,000. That's the equivalent of around 2,000 license fees.
News accounted for 43 of these occasions, at a cost of £174,500, excluding the use of private security teams.
BBC Vision, which produces the corporation's TV programmes, was behind the remaining 189, spending about £133,000, in most cases for consumer shows.
Thompson said these costs represented 0.011% of the news budget and 0.002% of the Vision budget over this period.
The inquiry heard there were two mentions of the BBC in the documents seized in the investigation into Whittamore's activities known as Operation Motorman.
In 2001 a current affairs journalist commissioned Whittamore to supply information about whether a paedophile was on a flight into Heathrow Airport.
The programme, which for other reasons was never broadcast, was looking at whether people with UK convictions for child sex offences could get jobs giving them access to children in other countries.
Thompson said: "The request to try and find out whether this particular paedophile was on the aircraft, I would regard as being justified in the public interest."
He added that the Motorman papers also included a reference to "BBC wine blag", which appeared to be an attempt by a newspaper to discover the corporation's spending on alcohol.
Whittamore's Hampshire home was raided by investigators from the Information Commissioner's Office in March 2003. He was convicted of illegally accessing data and received a conditional discharge at London's Blackfriars Crown Court in April 2005.
A BBC journalist also used a private investigator to find out the owner of a car from its number plate after the vehicle was used by someone suspected of involvement in a serious criminal conspiracy, the inquiry heard.
David Barr, counsel to the inquiry, suggested that this involved accessing private details from the DVLA's vehicle registration database.
Mr Thompson replied: "There were many different ways in which this information could be obtained."
He added: "It seems to me that it is an example where the technique used was justified in the context of the public interest journalism that was involved."
The director-general said in most cases the BBC used private detectives to provide surveillance or security in support of journalists.
But sometimes investigators are commissioned to track down the subject of a programme so they can be given a right of reply.
The BBC places a very high importance on allowing people time to reply to allegations against them, sometimes giving them as long as 10 days in the case of a complex financial investigation, the hearing was told.
The inquiry heard that Thompson 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.
It found no evidence that any of the corporation's staff had hacked phones or made improper payments to police officers.
The BBC sometimes makes small payments to politicians and police officers for appearing on programmes like Crimewatch, the hearing was told.
Thompson noted: "Occasionally a politician, or indeed anybody else, appears on an entertainment programme on the BBC or a comedy programme on the BBC. They might receive a fee."
During his evidence, Thompson was also asked about the incident on Radio 2 in which Russell Brand and Jonathan Ross made a series of crude phone calls to Fawlty Towers star Andrew Sachs.
"The Brand Ross incident was a lapse of editorial judgement," he said, adding that there has been a lively debate about the boundaries of comedy and taste for decades.
Thompson admitted that this incident "went far, far, far beyond the line", and exposed two issues - a lapse in judgement by "some senior people at the BBC" and problems with "compliance".
"Those systems were insufficiently secure," he said.
The director-general also gave evidence on the influence of politicians in media, highlighting Panorama's investigation into corruption at FIFA. According to Thompson, some politicians had made to case to him that broadcast of the programme might affect England's bid for the 2018 World Cup.
"I believe we were right to pursue the investigation," he said. "It would have been wrong to adjust the scheduling... I wanted to stand behind Panorama."
"Our job in serving the country is to tell the truth through our journalism," he added.