Sue Gray, the “partygate” investigator who went on to become Sir Keir Starmer’s chief of staff, has taken her seat in the unelected House of Lords four months after leaving the heart of Government.

Taking the title Baroness Gray of Tottenham, the former senior civil servant wore the traditional scarlet robes for the short introduction ceremony in the upper chamber, where she swore allegiance to the King.

She was supported by former Whitehall chief and independent crossbencher Lord O’Donnell and fellow Labour peer Baroness Harman.

Her son, Labour MP Liam Conlon, was among those watching the ceremony.

Sue Gray takes her seat in the unelected House of Lords with the title Baroness Gray of Tottenham (House of Lords/UK Parliament/PA)

While new peers are traditionally greeted with a handshake by the Leader of the Lords, Baroness Smith of Basildon, the 67-year-old received a welcome hug from the Lord Privy Seal as she left the chamber.

Lady Gray went from being an influential but little-known arbiter of conduct in government to a household name when she took on the probe into Covid rule-breaking at Boris Johnson’s Number 10 in 2021.

She stepped in to lead the investigation after then-cabinet secretary Simon Case, her boss, recused himself following allegations that his own office held a Christmas event amid a lockdown.

Civil Service impartiality was later thrown into question amid Conservative criticism of her move to quit the Cabinet Office after decades in Whitehall and join Labour as Sir Keir’s chief of staff.

Scrutiny of her new role mounted after the party won the election, with leaked disclosures that she earned more than the Prime Minister and reports of a power struggle in Downing Street between her and other aides.

After weeks of negative briefings against her, she announced her resignation in October in a statement citing concerns that she was “becoming a distraction” to the work of Government.

She was set to take up a newly created role as “envoy to the nations and regions” after a break from Government but Number 10 announced a month after her departure that she had decided not to take up the job.

Sue Gray investigated Covid rule-breaking at Number 10 in 2021 while Boris Johnson was prime minister (Aaron Chown/PA)

Lady Gray was among 30 new Labour peers who were announced last December by Downing Street as it sought to rebalance Parliament’s unelected second chamber.

A Labour source said at the time that the Tories had created an “imbalance” in the Lords which needed to be “corrected”.

Also taking her seat on the red benches was Joanne Cash, a barrister and co-founder of Parent Gym.

She was among six Conservative peers nominated by party leader Kemi Badenoch.

Dressed in the scarlet robes, Baroness Cash was supported by independent crossbencher Baroness Falkner of Margravine and Conservative peer Lord Godson as she swore the oath of allegiance to the monarch.