Labour is demanding that Rishi Sunak “come clean” about Suella Braverman’s security breach.
Ms Braverman resigned as home secretary under Liz Truss last week after violating the ministerial code by sending an official document from a personal email account. Rishi Sunak reappointed her on Wednesday.
Her reappointment has been criticized.
Labour’s Shadow Home Secretary Yvette Cooper said her party will try to “force the government to come clean”.
A number of sources have disputed Ms Braverman’s account of events.
So far new Prime Minister Mr Sunak has resisted demands to launch an inquiry into Ms Braverman’s security breach, despite Labour and the Liberal Democrats raising “national security” concerns and calling for a Cabinet Office probe.
Ms Braverman has also refused to appear before MPs to explain what happened.
Labour wants ministers to share risk assessments of this and other alleged leaks, as well as the information given to the prime minister before he put her back in the Home Office.
Shadow Home Secretary Yvette Cooper said Ms Braverman’s appointment “raises serious doubts” about the prime minister’s judgment and that the pair could not continue to hide from questions.
She continued: “People need to know they can trust the home secretary with highly sensitive information and our national security.
“Rishi Sunak’s decision to reappoint Suella Braverman was deeply irresponsible.
“Labour will use every parliamentary mechanism open to force the government to come clean over her reappointment, to get answers, and to require detailed documents to be released to the Intelligence and Security Committee.”
BBC News has spoken to several people with knowledge of the events surrounding Ms Braverman’s resignation.
A number of them dispute Ms Braverman’s claim to have reported her mistake to the cabinet secretary – the head of the civil service – as soon as she realised.
When confronted about her transgression she attempted to play down and explain away what had happened, sources suggested.
Ms Braverman had emailed a draft written ministerial statement on immigration policy to her close political ally, Conservative MP Sir John Hayes, using her personal email instead of her official government account.
Speaking to reporters on Friday, Labour leader Sir Keir Starmer demanded the home secretary was fired, accusing Mr Sunak of brokering a “grubby deal trading security for support” in the Conservative leadership contest.
But the prime minister insisted Ms Braverman had “learned from her mistake” and that he does not regret the appointment despite some Tory MPs adding also expressing concern.
Backbench MP Caroline Nokes backed opposition calls for an inquiry and former Tory chairman Sir Jake Berry described the breach as “really serious”.