Sue Gray is set to tell the government appointments watchdog when she first held talks with Labour about becoming Sir Keir Starmer’s chief of staff, according to reports.
Ms Gray, who has spent decades in the civil service, quit this week with immediate effect when news of her discussions with Sir Keir was leaked.
Allies of Boris Johnson and Conservative MPs have accused her of undermining the integrity of her own report into the “Partygate” scandal by taking the Labour job.
Ms Gray has now applied to the watchdog, which monitors the jobs taken by former ministers and senior mandarins, for permission to take up her new role.
The BBC reports that she will approach the watchdog about her new job on Monday.
Speaking on the Sunday with Laura Kuenssberg programme, shadow work and pensions secretary Jonathan Ashworth declined to give specifics after being asked when Ms Gray was offered the job.
But he said Sir Keir had been looking for a new chief of staff for "several weeks" and Ms Gray was "always going to be on the list."
However, a Labour source stressed to the BBC that "’on the list’ didn’t mean ‘in talks’."
Rishi Sunak will have the final say, although it remains unclear whether he has the power to block her from taking the job altogether.
Meanwhile the Cabinet Office has launched a probe into the circumstances of her unexpected resignation following concerns that none of her managers were told of the imminent switch.
Multiple Tory MPs responded with fury, while Mr Johnson’s backers suggested Ms Gray had shown herself to be politically motivated when she compiled the damning report into lockdown parties.
Ms Gray indirectly criticised the former prime minister in her report for "failures of leadership and judgment" during the pandemic, when No 10 and Cabinet Office staff were allowed to hold social gatherings while the general public was strictly banned from socialising.
She was the Government’s ethics chief for a number of years, leading investigations into the behaviour of multiple ministers who were accused of misconduct, and has also worked in Civil Service in Northern Ireland.
Ms Gray has never previously held a party-political role.
