Security services could be reluctant to share sensitive information with Suella Braverman after her controversial reappointment as home secretary, Lord Blunkett has warned.
The Labour peer, himself a former home secretary, suggested "there could be two really unfortunate outcomes to the reappointment of the current home secretary" just six days after she was forced to resign over a data breach.
"One is that the security and intelligence services will be reluctant to provide the briefings and the openness needed," he said.
"And the second is that other international security agencies will be reluctant to share with us if they are fearful that their information will be passed out of government itself."
Discussing the same issue on LBC on Wednesday night, Lord Blunkett described Ms Braverman's return to the frontbench as "an odd appointment with contradictions all the way down the line".
New Prime Minister Rishi Sunak is under growing pressure over reinstating Ms Braverman as home secretary after a former party chair claimed she had committed "multiple breaches" of the ministerial code.
Ms Braverman resigned her post just over a week ago after using her personal email address to forward sensitive government documents, breaking the rules that ministers have to abide by.
But the new prime minister put her back into the Home Office on Tuesday, and stood by the decision after being pressed on it in the Commons on Wednesday.
Later on Wednesday, former Tory Party chair Sir Jake Berry - who Mr Sunak fired from his post two days ago - told TalkTV: "From my own knowledge, there were multiple breaches of the ministerial code."
New Tory Party chair Nadhim Zahawi also defended Ms Braverman's appointment, telling Sky News: "People... are allowed a second chance."
But he would not deny that officials within the Cabinet Office warned against bringing her back due to the security breaches, saying: "Officials raise concerns and raise points... with ministers all the time, and I think they should be allowed to do that.
"And having discussions on air about what officials advise ministers I think would be unhealthy for the way we run our country because they should feel they can do that without being quoted in public."
Mr Zahawi said Ms Braverman "admitted her mistake", adding: "Redemption is a good thing."
Conservative MP Caroline Nokes said there were "big questions hanging over this whole issue", telling the BBC: "To be frank I would like to see them cleared up so that the home secretary can get on with her job.
"If that means a full inquiry then I think that's the right thing to do."
And fellow Conservative Mark Pritchard, a former member of parliament's intelligence and security committee, said a "breakdown" in trust between security services and Ms Braverman must be "sorted ASAP".
Shadow foreign secretary David Lammy called for a full investigation into Ms Braverman's actions and for her to be sacked, telling Sky News: "The home secretary is the most serious job you could have in our state.
"This is a person who makes judgements about terrorism and counter-terrorism, who makes judgements about very, very serious offenders, whether they should be allowed out of prison, and for that reason, it's someone who, I'm afraid, judgement is critically important.
"I'm afraid this is a lapse of judgement that, quite rightly, she was sacked for. The question is, why was she brought back?"
During PMQs yesterday, Labour leader Sir Keir Starmer accused Mr Sunak of having done a "grubby deal" with Ms Braverman - a figure popular on the right of the party - in order to secure the keys to Number 10.
But asked whether Mr Sunak believed MI5 was confident in Ms Braverman as home secretary, the PM's official spokesperson told reporters on Thursday: "Yes, the home secretary continues to have strong relationships with all the operational bodies that report into the Home Office and are focused very much on keeping the country safe."