Calls demanding an investigation into Suella Braverman’s reappointment as Home Secretary intensified on Wednesday.
Labour has joined the Liberal Democrats in calling for an urgent probe.
Ms Braverman stood down from the top job at the Home Office a week ago after breaching the ministerial code by sending a sensitive papers from a personal email as she was embroiled in a row with then premier Liz Truss over immigration.
She was reappointed by new Prime Minister Rishi Sunak on Tuesday.
Shadow home secretary Yvette Cooper called for a full investigation into Ms Braverman’s actions and “other possible security breaches”.
In a letter to Cabinet Secretary Simon Case, she said: “It must include the extent of the Home Secretary’s use of private email accounts to circulate Government papers and the extent to which official documents have been sent outside Government, as well as any other concerns that have been raised about possible serious information and security breaches by Suella Braverman.”
The Liberal Democrats have also called for a Cabinet Office inquiry into the appointment.
The party’s Home Affairs Spokesperson, Alistair Carmichael MP said: "Suella Braverman's appointment makes a mockery of Rishi Sunak's claims to be bringing integrity to Number 10.
"If it is confirmed that Suella Braverman repeatedly broke the ministerial code and threatened national security, she must be sacked.”
Foreign Secretary James Cleverly defended the re-appointment of Ms Braverman on the grounds that she had apologised for a mistake which forced her to resign from the same post just days ago.
It had been heavily criticised and Mr Cleverly was grilled on it when he appeared on Sky News given that new PM Rishi Sunak had vowed to put “integrity, professionalism and accountability” at every level of his Government.
Mr Cleverly responded: “She has said that she made an error.
“She has apologised for that and the Prime Minister has clearly taken the apology in the manner that she wanted to put across.
“She has shown a willingness to take responsibility for what happened but ultimately he has decided that he wants to see the agenda that she has set out, that very important crime-fighting agenda.”
Mr Braverman, a senior figure on the Tory Right, is seen to have been a crucial backer for Mr Sunak as he and Boris Johnson were still locked in a race for the Tory leadership and to be the next Prime Minister.
Mr Cleverly brushed aside the suggestion that her support for Mr Sunak at this key time led to her being given back her job as Home Secretary, stressing that he did not need the support of any one MP.
While her re-appointment has been welcomed by the Tory Right, it was immediately criticised by Labour, as well as immigrant and refugee campaign groups.
Shadow education secretary Bridget Phillipson said it "tells you everything that you need to know about this Government".
She told BBC Radio 4's Today programme: "One moment Rishi Sunak is telling us he will lead a Government of integrity, and then another minute he's appointing someone back into the Cabinet who'd been sacked only the week before for a serious breach of security and a potential breach of the ministerial code.
"It was a grubby deal that he struck in order to get over the line and become Prime Minister.”
Ms Braverman originally left the role last week after she said she had made a "technical infringement" of the rules by sending an official document from a personal email and was now taking responsibility.
Her exit made her the shortest-serving Home Secretary in modern political history.
