Sir Keir Starmer has dodged questions about when Labour first approached partygate investigator Sue Gray with the offer of a senior role.

It comes amid a furious reaction from Boris Johnson and his allies to the news that Ms Gray is planning to become the Labour leader’s chief of staff, as he sought to use her move to discredit the Privileges Committee inquiry into whether he lied to the House of Commons over lockdown breaches.

The Labour leader, who visited Londonderry on Friday after Rishi Sunak secured his Windsor Framework deal earlier this week, batted away questions about when conversations first began with the high-profile Whitehall civil servant.

Sir Keir said it had been “known for some time” that he was hoping to appoint a chief of staff, but refused to get into specifics when pressed by broadcasters.

“I think it has been known for some time that I have been looking for a chief of staff and I am very focused on what it is I need from a chief of staff,” he said.

The Labour leader, whose party maintains a significant lead against Mr Sunak’s Conservatives, linked her planned appointment to ongoing preparations for government after the next election.

He also robustly defended her reputation, stressing that he was delighted “really strong professional, respected individuals” want to join Labour.

Under the civil service code, officials of Ms Gray’s seniority must wait a minimum of three months before taking up outside employment.

The move will be scrutinised by Parliament’s anti-corruption watchdog, the Advisory Committee on Business Appointments (Acoba), with Ms Gray expected to await the Acoba decision before starting the role.

Parliament’s anti-corruption watchdog can advise waiting periods before civil servants take on other jobs and the Prime Minister ultimately makes the final decision.

But Downing Street made it clear that Mr Sunak cannot block her from taking a job.

“I am delighted that respected, professional individuals want to be part of what we are doing in the Labour Party,” Sir Keir said.

“We are a changed Labour Party and I am very well aware that we have got to earn every vote going into the election, but we won’t be forgiven if we are not prepared for government.

“We are going to inherit a very badly damaged country, damaged economy, damaged public services and I want to ensure we are in a position to deliver for the whole of the United Kingdom and that is why I am so pleased that people of real quality, really respected… want to join the team.”

He also appeared to reject any suggestion the move threatened to undermine the Privileges Committee investigation.

“I think Boris Johnson needs to confront the evidence that is there in front of him and everybody can see that evidence,” he said.

“Rishi Sunak needs to acknowledge that he actually sat on his hands through this process.”