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Ex-detectives who disclosed that legal pornography was found on Damian Green's office computer were in "flagrant breach" of their code of conduct, a former attorney general has said.
Dominic Grieve said their actions smacked of the "police state".
However, a former chief constable told the BBC the information was in the public interest.
First Secretary of State Mr Green denies watching or downloading pornography on his computer.
Tory MPs, including Brexit Secretary David Davis, have backed Mr Green – effectively Theresa May's second-in-command – saying it was wrong for such claims to emerge through the media.
The allegations were first raised last month by former Met assistant commissioner Bob Quick, who led a 2008 inquiry into Home Office leaks which saw Mr Green's Commons office being searched.
He made the claims after the Cabinet Office launched an investigation into accusations of inappropriate behaviour by Mr Green towards journalist Kate Maltby, which the MP has described as "completely false".
'Very worrying'
On Friday, retired Scotland Yard detective Neil Lewis told BBC News "thousands" of thumbnail images of legal pornography had been found on Mr Green's parliamentary computer in 2008.
Scotland Yard has confirmed its department for professional standards was examining allegations that Mr Lewis had disclosed confidential information.
And speaking on BBC Newsnight, Mr Grieve described the decision by the officers to release such information from a police investigation as "very worrying".
"They choose to put material that an ordinary citizen would be prohibited from acquiring under data protection rules into the public domain on their own judgment."
Mr Grieve, attorney general in David Cameron's government between 2010 and 2014, said: "If you think something is relevant you do it by proper official means. You do not go freelancing as these two officers have done…
"We give the police powers that other people do not have. They are not and must not be allowed to abuse those powers."
Former Gloucestershire chief constable Tim Brain defended the officers on Newsnight, saying they had come forward with what they considered "relevant information" to an ongoing inquiry.
Mr Brain added: "Let's just think about this as a workplace computer and to think whether we are happy that people, our MPs, can have this kind of material on what is an official computer…
"We need to have some answers now this information is in the public domain."
'Willing to resign'
On Friday, sources close to David Davis told the BBC the Brexit Secretary had warned Downing Street not to sack Mr Green as a result of a "wrongful attempt by former officers to do him down".
One said Mr Davis might be willing to resign over the issue, although another stressed no threat had been made.
"It's right that allegations of misconduct towards individuals are properly investigated," said an associate of Mr Davis. "But police officers have a duty of confidentiality which should be upheld".
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What is the row all about?
- The allegations date back to November 2008 when the Conservatives were in opposition and Damian Green was their immigration spokesman
- He embarrassed the Labour government with a series of leaks about illegal immigration and other issues
- Police raided his Parliamentary office as part of an inquiry into how he got his hands on confidential documents
- His office computer was seized and he was detained for nine hours – sparking fury among Tory MPs
- No charges were brought against the MP or civil servant Christopher Galley, who passed unauthorised material to Mr Green, although the official was sacked
- The officer in charge of the inquiry, Bob Quick – widely criticised by Tory MPs for the raid – resigned six months later over an alleged security breach
- But a month ago, Mr Quick disclosed that pornographic material had been found on the seized computer, adding that the police had not pursued the matter at the time or told Mr Green about it
- The matter has since been investigated by the Cabinet Office as part on a wider inquiry into claims of inappropriate behaviour by Mr Green towards journalist Kate Maltby
- The inquiry is believed to centre on the ministerial code, which sets out the standards of conduct expected of government ministers.
Other MPs to criticise the action of the former officers included the chairman of the Commons culture committee Damian Collins.
He told BBC Radio 4's Any Questions the "Cabinet Office is running that investigation. They should receive and see any evidence that's pertinent to it."
The DUP's leader at Westminster, Nigel Dodds, said "police are not above the law" and their actions had been "totally wrong".
Speaking to reporters at his Kent home on Friday, Mr Green said: "I have maintained all along and I still maintain – it is the truth – that I did not download or look at pornography on my computer, but obviously while the investigation is going on, I can't say any more than that."
