Former Crimewatch presenter Jacqui Hames tells the Leveson inquiry the News of the World was involved in an attempt to "subvert" a murder investigation.
The former Scotland Yard detective fought back tears as she claimed she had been put under surveillance by the newspaper because of its links to suspects in a notorious murder case.
The inquiry into press standards was told that she and ex-husband Dave Cook, who was also a former Metropolitan Police detective, had been followed by private investigators.
Ms Hames said this followed an appeal Mr Cook had made on Crimewatch in 2002 asking for information about the 1987 murder of private investigator Daniel Morgan.
She alleged that Mr Morgan's firm, Southern Investigations, whose members included suspects in the killing, had "close links" to senior News of the World news editor Alex Marunchak.
She said in a statement to the inquiry: "I believe that the real reason for the News of the World placing us under surveillance was that suspects in the Daniel Morgan murder inquiry were using their association with a powerful and well-resourced newspaper to try to intimidate us and so attempt to subvert the investigation.
"These events left me distressed, anxious and needing counselling, and contributed to the breakdown of my marriage to David in 2010. Given the impact of these events, I would like to know why the police did not investigate why we came to be placed under surveillance by a newspaper like this."
Shortly after the Crimewatch appeal, police colleagues are said to have informed Mr Cook he was being targeted by journalists at the News of the World.
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When Mr Cook met the News of the World's then editor Rebekah Brooks she suggested the surveillance was carried out because the tabloid suspected that they were having an affair with each other.
But Ms Hames told the inquiry that this was "absolutely pathetic" because she and Mr Cook were well known as a couple within the force and had appeared in Hello magazine together.
Ms Hames told Channel 4 News in July 2011 that she felt "hunted" by private investigators alleged to be working for the News of the World.
At the time she said she was "convinced" that her confidential police personnel file was sold to private investigator Mulcaire, who worked for the News of the World.
Ms Hames told the inquiry she was "extremely proud" to have served in the Metropolitan Police. But she was overcome by emotion as she added: "When someone in your family or the police service has sold you down the line it is very hurtful, very painful."
The other witness who appeared this morning was Liberal Democrat deputy leader Simon Hughes, who in his evidence claimed that he was aware of at least three other journalists who were giving Mulcaire orders.
Joanna Yeates' murder
Another witness was Christopher Jeffries who sued a number of tabloid newspapers for libellous allegations made while he was being questioned in connection with Bristol landscape architect Joanna Yeates' murder. He was released without charge and Vincent Tabak was later convicted of the murder.
The latest round of evidence follows the appearance on Monday of the police officer leading the investigation into alleged illicit payments by the Sun.
Deputy Assistant Commissioner (DAC) Sue Akers said payments had been made to officials in "all areas of public life" and sometimes amounted to tens of thousands of pounds.
Meanwhile, it has emerged that Scotland Yard chiefs loaned a police horse to Ms Brooks. The force has confirmed that the former News International chief executive "fostered" the animal after it retired from active service.
She paid for food and vet bills until it was rehoused with a police officer in 2010 - months before fresh investigations into illegal activities at the News of the World.
A Metropolitan Police spokesman said Ms Brooks, a riding enthusiast, was first given permission to take charge of the horse in 2008.
09 February 2012