Suella Braverman has been accused of "multiple breaches of the ministerial code" as Rishi Sunak faces a backlash over reinstating her as Home Secretary.
Former Conservative Party chairman Jake Berry, who left his role on Tuesday, took to the airwaves to attack the decision by the new Prime Minister.
Braverman admitted to a "technical infringement" of the rules as she was forced out prior to Liz Truss 's downfall, making her then the shortest-serving home secretary in history.
Speaking to TalkTV's Piers Morgan Uncensored, Berry said: "From my own knowledge, there were multiple breaches of the ministerial code."
Braverman left her role in Truss's cabinet after she was caught sending veteran backbench Tory Sir John Hayes, a fellow right-winger, an official document from a personal email account.
She accidentally copied in someone she believed was Sir John's wife, but was in fact an aide to Conservative MP Andrew Percy, who raised the alarm. Braverman argued it was merely a draft written ministerial statement on immigration which had been due for publication imminently.
Allies said she sent it after going on a 4am immigration raid before coming clean about her "mistake". One told PA: "She was not expecting at all to be sacked over it."
But officials said the file was sent much later and that the Cabinet papers had first been forwarded from her ministerial account to a private Gmail account before going elsewhere.
Berry told TalkTV: "It was sent from a private email address to another Member of Parliament. She then sought to copy in that individual's wife and accidentally sent it to a staffer in Parliament.
"To me that seems a really serious breach, especially when it was documents relating to cybersecurity, as I believe. That seems a really serious breach. The Cabinet Secretary had his say at the time. I doubt he's changed his mind in the last six days, but that's a matter for the new Prime Minister."
Braverman said she "rapidly reported" her "mistake" through official channels, and informed Cabinet Secretary Simon Case, as soon as she realised it.
But Berry said: "As I understand it, the evidence was put to her and she accepted the evidence, rather than the other way round."
Labour has demanded that Case, who is reportedly "livid" over her swift return and "very concerned" about the breach, launch an investigation "into the extent of this and other possible security breaches".
New Tory chairman Nadhim Zahawi defended Sunak's decision to give Braverman a "second chance". The Prime Minister has faced criticism over his decision to reappoint her to the post just six days after she was forced to resign over a security breach.
Zahawi told Sky News: "She admitted her mistake, she resigned. A new Prime Minister came in, looked at the information and decided that he wants to give her a second chance. It think that is the right decision. Redemption is a good thing."
Zahawi refused to be drawn on reports that officials, including the Cabinet Secretary Simon Case, expressed concern about her reappointment so soon after her resignation.
"Officials raise concerns and raise points with secretaries of state, with ministers, all the time. I think they should be allowed to do that," he said.
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