A private investigator employed by the Sun has said he illegally accessed the Duchess of Sussex’s private information shortly after she met Prince Harry.

Dan Hanks, who lives in Los Angeles, told the website Byline Investigates that he compiled a 90-page report on the future member of the royal family in October 2016, shortly after the tabloid newspaper first became aware of her relationship with the prince.

The information sent to the Sun’s US editor allegedly included relatives’ phone numbers, background information on her ex-husband, and also Meghan’s personal social security number. Although much of the information could have been obtained legally, Hanks claims he took it from a database that could not legally be used for journalistic purposes.

Hanks told the New York Times that the the Sun made him sign a letter stating he would not use any illegal methods to locate people or do background checks: “Then the reporters came back to me and said, ‘But if you want to get work, keep doing what you’ve been doing,’ with a nod and a wink.”

The Sun strongly denies this and said it had a written agreement with Hanks that he would not break the law while working for the news outlet and did not know he had done so. The newspaper’s publisher said they stopped using Hanks’ services in 2017 after he was sent to jail after being found guilty of extortion in an unrelated case.

The Duke and Duchess of Sussex have been at war with the British tabloids over the last two years, with Meghan successfully suing the Mail on Sunday after it published a private letter she sent to her estranged father. Their interview with Oprah Winfrey has also started a national conversation about racism in the British media that has claimed the jobs of both Piers Morgan and the boss of the Society of Editors, the media industry body.

Prince Harry is pursuing phone hacking legal cases against the publishers of both the Sun and the Mirror.

A spokesperson for the couple said: “The Duke and Duchess of Sussex feel that today is an important moment of reflection for the media industry and society at large, as this investigative report shows that the predatory practices of days past are still ongoing, reaping irreversible damage for families and relationships.

“They are grateful to those working in media who stand for upholding the values of journalism, which are needed now more than ever before.”

Byline Investigates, which tracked down Hanks, is run by Graham Johnson, a freelance journalist who was himself convicted for phone hacking but now works to expose other examples of historical wrongdoing in the media. Byline said it paid Hanks to obtain the archive reports on Meghan which form the basis of its story.

A spokesperson for News UK, publisher of the Sun, said: “In 2016, The Sun made a legitimate request of Mr Hanks to research contact details and addresses for Meghan Markle and possible relatives using legal databases which he had a license to use. He was paid $250.

“Mr Hanks was not tasked to do anything illegal or breach any privacy laws – indeed he was instructed clearly in writing to act lawfully and he signed a legal undertaking that he would do so. The information he provided could not and did not raise any concerns that he had used illegal practices to obtain the information.

“At no time did the Sun request the social security number of Meghan Markle, nor use the information he provided for any unlawful practice. The Sun abides by all laws and regulations and maintains strict protocols in relation to the obtaining of information from third parties. Strict compliance is in place to cover all our reporting.”