Most of the Hackgate coverage has been about alleged illegal behaviour by News of the World journalists and the private detective it employed, Glenn Mulcaire.
However, there is a related issue which will be probed by Lord Justice Leveson, who has been asked by the prime minister to examine the culture, practices and ethics of the press.
According to sources close to Lord Justice Leveson, he will be looking at the extent to which newspapers used private detectives instead of journalists to ferret out information.
He is expected to take a view about whether this is an appropriate way to behave, and whether readers should be informed that stories have been obtained by hired detectives rather than through more conventional journalistic enquiries.
It is in that context that the BBC has been investigating the employment by the Daily Mirror in the late 1990s of a controversial firm of private detectives, Southern Investigations, whose boss Jonathan Rees was jailed in 2000 for conspiring to plant cocaine on an innocent person.
What the BBC has learned is that Southern Investigations was employed by the Daily Mirror and Sunday Mirror on 230 occasions between 7 October 1997 and 23 September 1999. The total sums billed to the Mirror by Southern Investigations were just under £67,000. ..read more