Two former Cabinet ministers have raised concerns about the proposed appointment of Australian Carol Mills as Parliament's senior official.
Former foreign secretaries Jack Straw and Dame Margaret Beckett have added their voices to a cross-party campaign for Ms Mills to face a confirmation hearing in front of MPs before she can take up the role.
Meanwhile Ms Mills has broken her silence over an email from the Australian clerk of the Senate, Rosemary Laing, which warned that she had no "parliamentary knowledge or experience" and should not be appointed.
Ms Mills, head of the Department of Parliamentary Services (DPS) in Canberra, is believed to have been recommended for the prestigious role following a recruitment process with a selection panel led by Speaker John Bercow.
She said he was "disappointed" to read the missive from Ms Laing.
"It would not be appropriate for me to comment further in a personal capacity at this time," she said.
"As a senior parliamentary officer, I take seriously my responsibilities to promote and uphold the values and code of conduct articulated in the Commonwealth of Australia Parliamentary Service Act 1999."
Ms Laing apparently cited an incident in which the Australian Department of Parliamentary Services confirmed it had used CCTV cameras to retrace the movements of a DPS employee and show her pushing an envelope under the door of a senator's office late at night.
The episode has been referred to the Senate privileges committee for inquiry, as cameras are supposed to be used only for security and to prosecute illegal activity.
But in her statement, Ms Mills said the DPS "looks forward to the opportunity to explain to the committee the basis of its view that use of the CCTV footage was in fact authorised, and wholly consistent with parliamentary privilege".
Referring to the Westminster role, she said: "I have obviously seen media coverage in recent weeks about recruitment to the role of the clerk of the House of Commons and chief executive officer of the House of Commons service.
"I have declined to confirm or comment upon my candidacy to date, as the selection process has not concluded."
Concerns have been raised about Ms Mills's ability to fulfil the role as adviser on parliamentary procedure and constitutional matters, with former speaker Baroness Boothroyd previously warning she would be "totally out of her depth".
In response to Ms Mills's statement, Lady Boothroyd said it was a further reason for the appointment to be postponed.
Ms Mills's name is understood to have already been put forward to David Cameron to subsequently recommend to the Queen.
But Lady Boothroyd said: "Her statement underlines the urgent need for the Prime Minister to reconsider her proposed appointment as clerk of the House of Commons.
"The inquiry by the Australian Senate into the conduct of the department she currently heads in Canberra raises further questions which will take time to answer, which is right and proper."
"Mr Cameron should postpone a decision until widespread concerns about her suitability to fill an important constitutional position at Westminster are properly addressed."
Public Administration Committee chairman Bernard Jenkin has called for Ms Mills to face a pre-appointment hearing, a move backed by Mr Straw and Dame Margaret .
Mr Straw, a former leader of the Commons, told The Guardian: "Given the controversy, and without making any observations about the relative merits of the candidate, I think that such pre-appointment scrutiny would be a good way of resolving this."
Dame Margaret, who also served as leader of the Commons, told the newspaper: "These days you cannot make an appointment like this without select committee scrutiny."
The £200,000-a-year position combines the constitutional role of clerk of the House of Commons with being the chief executive responsible for running the building and managing almost 2,000 staff.
Dame Margaret said: "The idea of having a chief executive role, which is not the clerk to the House, has often been discussed in the past.
"But as far as I know the house has never decided actually to go down that road. It is a step of perhaps major constitutional significance as far as the house as a whole is concerned."
Tory MP Dan Byles said on Twitter: "Pressure to hold a pre-appointment hearing for #CarolMills is growing. This seems like a very sensible way forward."
It was a view echoed by fellow Tory Sarah Wollaston, who said a pre-appointment hearing was "essential".
Mr Bercow - who has attempted to drive a significant modernisation of the Commons - has come under fire for overlooking the respected deputy clerk David Natzler for reasons of political correctness.
But his allies have defended the way the process was handled, with an open recruitment process and lengthy interviews for the shortlisted candidates.
Mr Bercow chaired the appointment panel which also included the Commons leader Andrew Lansley, shadow leader Angela Eagle, Labour chairwoman of the Public Accounts Committee Margaret Hodge and Liberal Democrat John Thurso.
Parliamentary and Health Service Ombudsman Dame Julie Mellor was the external panel member.
Mr Bercow's spokeswoman said: "This is the first time ever there has been an open and fair recruitment process for the clerk of the House of Commons."
Eight candidates were interviewed, with a shortlist of three called back for a second round of grilling by the panel.
The Speaker's spokeswoman said the candidates were "scrutinised very carefully indeed".
The vacancy has arisen because of the retirement of Commons veteran Sir Robert Rogers amid claims he has clashed with the Speaker.
Tory MP Michael Fabricant, who claimed in the Commons last month that Mr Bercow had once told Sir Robert to "f*** off" in front of witnesses - an allegation immediately denied by Mr Bercow - said the Speaker should consider resigning.
On Twitter he said: "If I were #Bercow, I'd be thinking about my own position, let alone considering what to do about the rigged appointment of the new Clerk."
Sir Robert has put in place a plan for when he retires at the end of the month, with Mr Natzler acting up as clerk until the new appointment is in place and Dame Janet Gaymer chairing the Commons management board.
He told BBC2's Newsnight that the arrangement could remain in place for months if wrangling over his replacement continued.
He said the plans "are resilient" and that "we could go to the election without a problem. I'm quite sure we would be fine".
Senior Liberal Democrat Sir Alan Beith, chairman of the Justice Select Committee, has written to Commons leader William Hague urging a pause on the appointment.
"Although the roles of Procedural adviser and Chief Executive could be split, the House has not made any decision to do so, and opinion is probably very divided on that issue," Sir Alan said.
"There is a real fear that the job of Clerk of the House is being changed without consultation with MPs and Committee Chairs."