Alastair Campbell has accused Piers Morgan, the Daily Mirror’s former editor, of being “two-faced” as he claimed his mortgage details were illegally obtained in an attempt to destabilise the then Labour government.

Tony Blair’s former spin doctor told the High Court he was a victim of unlawful information-gathering by Mirror Group Newspapers (MGN) when journalists targeted “private and personal financial information” about himself and Fiona Millar, his partner.

He said Morgan purported to be a “real ally” of Mr Blair and the Labour government while “all the time he and his senior team were using illegal means to find stories designed to destabilise that Government”.

“Mr Morgan’s two-faced conduct…compounds the anger I feel about this,” he added.

Mr Campbell was called to the witness stand on Tuesday to testify in support of Prince Harry and other claimants in their case of alleged unlawful information gathering against the publishers of the Daily Mirror.

He claimed in his witness statement that it was “extremely troubling” that MGN journalists unlawfully obtained information about himself and Ms Millar, especially due to his “role in government at the time”.

Mr Campbell, who worked as chief press secretary in Downing Street from 1997 to 2000, said he was “disgusted” at the methods used by MGN to obtain his mortgage details and those belonging to Peter Mandelson when he was a Cabinet minister.

He said that they were obtained by Southern Investigations, a private detective agency, as suggested in two invoices from the company addressed to the Mirror’s Gary Jones.

Mr Campbell said he was shown three documents from the claimants’ legal team including the invoices from Southern Investigations.

One invoice was titled “A J Campbell and Fiona Miller [sic]” and was a £150 payment “for undertaking confidential enquiries and reporting our findings in detail”. The second had the same reference and date and was for £275.

The third document, which was confidential, contained written information about Mr Campbell and Ms Miller’s mortgage payments, including the exact amount of the monthly payments coming out of the couple’s bank accounts.

He said the document had been seized by the police in a raid on Southern Investigations in 1999 and that it was disclosed by a “confidential source” of journalist Graham Johnson.

Mr Campbell, who was political and assistant editor at the Daily Mirror in the early 1990s, said in his statement: “Fiona and I are shocked, and frankly, appalled at this intrusion into our privacy by the Daily Mirror.

“I find it very hard to believe that any editor, especially one as hands-on as Mr Morgan, would not have known and demanded to know where the big stories were coming from.

“Nor do I believe that people in senior positions in government with access to highly sensitive information and with obvious security concerns would have been targeted in this way without the editor knowing and sanctioning such methods.”

Mr Campbell said that he never witnessed any phone hacking incidents while working at the Daily and Sunday Mirror.

Asked by Andrew Green KC, representing MGN, whether he would have spoken out had he been made aware of phone hacking or unlawful information gathering for stories, he replied he would have done.

Mr Campbell told the court: “I was based in Westminster most of the time but I think I would have known about it because I don’t think any of the editors I worked for at the time would have sanctioned it”.

He said that a “handful” of journalists reported to him in Westminster, but insisted that there was “never-ending contact” with the other editors in the newsroom.

Meanwhile, Vijay Vaghela, Trinity Mirror group’s former finance director said in his witness statement that he did not know about unlawful information-gathering by MGN journalists before the litigation.

He told the hearing that he was aware of private investigators being used to source stories for MGN, but that he did not know anything about why or how they were being used.

“I believed that editorial had appropriate controls on how stories were being sourced,” he said.

Mark Lewis, a media lawyer who led the fight against phone hacking claims that brought down the News of the World, also took to the witness stand.

In his statement, he claimed that he too was targeted by journalists at MGN.

He said he was shown invoices from two private investigators with the subject “M Lewis”, one of which was sent in July 2005 claiming £129.26 for “urgent enquiries”.

During cross-examination, Mr Green argued that Mr Lewis does not have “a single shred of evidence that your phone was hacked by MGN in 2001 or any other time”.

The case continues.