NoW hired ex-policeman to track hundreds of people
A dossier of evidence obtained by BBC Newsnight from an ex-policeman hired by the News of The World (NoW) shows the newspaper was engaged in covert surveillance on a huge scale.
Over eight years Derek Webb was paid to follow more than 100 targets.
They included Prince William, Prince Harry's ex-girlfriend Chelsy Davy, former attorney general Lord Goldsmith and football manager Jose Mourinho.
The paper's owner News International said it was not able to comment.
Along with celebrities like football pundit Gary Lineker, relatives of stars - such as the parents of Harry Potter actor Daniel Radcliffe - were also targeted.
Mr Webb says he is not ashamed of his actions and that he did nothing illegal.
It comes a day after revelations that the NoW hired Mr Webb to carry out surveillance on two prominent lawyers representing victims of phone hacking. One of the lawyers, Mark Lewis, is to take legal action against News International.
Speaking exclusively to Newsnight's Richard Watson, Mr Webb said that shortly after setting up his own private detective agency in 2003 he was contacted by the NoW and offered work.
He continued to work for the newspaper until it was shut down in July after a string of allegations emerged about the hacking of phones, including that of murdered schoolgirl Milly Dowler.
"I was working for them extensively on many jobs throughout that time. I never knew when I was going to be required. They phoned me up by the day or by the night... It could be anywhere in the country."
Mr Webb is a former police officer who worked for many years in covert surveillance and received additional training from MI5.
He said he felt the paper should have given him "loyalty money" for his eight years of service when it closed - as it had done for other freelancers - but it refused.
Mr Webb said that most of the time he received his commissions over the phone, but sometimes he was also e-mailed photographs or address details to assist him in his work.
The approaches came from a number of journalists at the paper, he said.
The private detective said that 90% of his targets were celebrities or politicians.
They also included Boris Johnson, Angelina Jolie, Simon Cowell, Sir Paul McCartney, Charles Kennedy, David Miliband, Elle MacPherson and Heather Mills.
In 2006, Mr Webb was asked to follow Prince William when the prince was spending a number of days in Gloucestershire.
It was also in 2006 that Mr Webb covertly followed Gary Lineker, a job which lasted a number of weeks.
Lord Goldsmith was followed by Mr Webb when he was attorney general for England, Wales and Northern Ireland.
And on occasion the surveillance was not restricted to celebrities or public figures, but the people that surrounded them - Mr Webb's records show that in the last two years he was hired to follow the parents of Daniel Radcliffe.
Newsnight's Richard Watson said the "industrial scale" of the surveillance was "astonishing" and it raised ethical issues about what the NoW was doing to get exclusive stories.
Mr Webb kept detailed logs of his movements and observations while on surveillance jobs, which Newsnight has seen.
"Basically I would write down what they were wearing at the time, what car they were in, who they met, the location they met, the times - the times were very important - and I would keep that.
"And then I would transfer part of it into my diary, but not the actual log itself. Just the names of the people."
Mr Webb said he never asked his contacts at the newspaper why they had selected the targets for surveillance.
He also defended his work for the newspaper, pointing out that what he had done was legal.
Mr Webb went on: "I don't feel ashamed. I know to a certain extent people's lives have been ruined with front page stories but... if I wasn't doing it, somebody else would have been."
A Downing Street spokesman said the issues raised would be a matter for the Leveson judicial inquiry into phone hacking, which is due to start on Monday and will look at the culture, practices and ethics of the press.
Asked about the security implications surrounding surveillance of a member of the royal family, he said Downing Street did not comment on matters of security.
Shadow culture secretary Harriet Harman said: "This covert surveillance by News of the World was out of control. Lord Leveson's inquiry will need to identify the full extent of it and get a grip on it."
The Press Complaints Commission said it would examine the full details of the claims, and asked News International to clarify its own position on what has happened.
A News International spokesman said: "We are not able to make any comment around the specific work carried out by Derek Webb.
"As is well known, The News of the World was closed by News International during the summer."
Former News of the World features editor Jules Stenson said Mr Webb was clearly a man with a grudge and only his side of the story was being heard.
"You're only hearing a very slanted story and you're hearing no context to these investigations," he told Newsnight.
The revelations come as News International chairman James Murdoch prepares to face MPs on the Commons culture, media and sport select committee on Thursday, to answer questions about his knowledge of illegal activities by his employees.
In a separate development, documents released by the committee showed News International's owners News Group continued to pay legal fees for former NoW royal correspondent Clive Goodman - jailed in 2007 for phone hacking - as recently as April 2010.
Mr Goodman received £9,631.50 to cover legal fees between February and April last year, the company's lawyers Linklaters said.
The solicitors also confirmed Mr Goodman had been paid three months' salary, totalling £22,504, following his guilty plea to hacking charges, including £7,500 after he was dismissed. He received further payments totalling more than £240,000 later in 2007.
Watch Richard Watson's full report on the BBC iPlayer and Newsnight website.