Gordon Brown has called on the police to launch a criminal investigation after a private investigator employed by the Sunday Times for 15 years said he had gained access to his bank and mortgage accounts by deception.

The former prime minister claimed that “25 to 40 violations of the law” took place in pursuit of a story relating to his purchase of a flat that was published in early 2000 under the editorship of John Witherow, who now edits the Times.

Brown released a statement on Thursday night saying that there had been “new evidence” from John Ford, who earlier this month said he had penetrated the then chancellor’s bank and mortgage accounts at the behest of the Sunday broadsheet.

The former MP said: “I believe that the police should now investigate these criminal acts,” and he hinted at further legal or political action if necessary. “We are considering all avenues to expose the wrongdoing,” he added.

Brown said he had talked to the editor as the article was close to publication. “I talked directly to John Witherow about the story on my flat on the night it appeared. He was fully aware of the details of the story.

“We now know that under his editorship, at least 25 to 40 violations of the law took place to write the story, with the intention of forcing me out of office.”

The Sunday Times has previously said it was investigating if there was anything suspicious in the purchase of a property by Brown in 1992 from the estate of the controversial former owner of the Daily Mirror, Robert Maxwell.

Nothing untoward was found, although the newspaper did publish a story noting that Brown purchased Maxwell’s flat, saying he had paid £30,000 less than the prevailing market price in the area at the time.

Brown bought the flat from Arthur Andersen, the accountants acting as administrators for the collapsed Maxwell companies. The administrators insisted at the time that the flat had been sold on the open market at “the best available price ... at a time of serious property depression”.

When he recounted his part in the episode last month, Ford said he regretted what he had done: “What right did I have to look at the chancellor’s bank account to stand up a non-story?”

Blagging – using deception to obtain private information from banks, mortgage companies or utility firms – is illegal under the Data Protection Act 1998, which came into force in March 2000. There is an exemption for newspapers if private information is held or obtained for the purpose of journalism with a view to publication and with a reasonable belief that the publication is “justified in the public interest”.

Prior to that, with effect from February 1995, a specific offence of obtaining unauthorised access to personal data by deception was added to the 1984 Data Protection Act, which at that time had no exemption for the press.

In January 2012, Witherow told the Leveson inquiry that somebody acting on behalf of the Sunday Times had pretended to be Brown in order to obtain information from his mortgage account held by Abbey National as part of the investigation.

The editor was not asked about Brown’s bank account, although an earlier article published by the Sunday Times in July 2011 had said: “The Sunday Times never broke into his bank account.”

In the statement released on Thursday Brown also accused Witherow of having “misled the Leveson inquiry when he claimed the Sunday Times had not broken into my account”.

A spokesperson for the Sunday Times said: “The Leveson inquiry dealt with this matter in a public forum in 2012. We have nothing further to add.”