Head of the civil service Simon Case is reportedly among those to have received a questionnaire from police investigating allegations of lockdown-breaking parties.
The Cabinet Secretary had been tasked by Boris Johnson to investigate the events held in Downing Street and wider government.
But he was forced to stand down from the inquiry and was replaced by senior civil servant Sue Gray when it emerged that a gathering had been held in the Cabinet Office.
Now the Financial Times reports that Mr Case is among the more than 100 people to have received questionnaires from the Metropolitan Police.
Neither the Cabinet Office nor Downing Street denied he was being questioned in the Scotland Yard inquiry opened as a result of information passed to officers by Ms Gray.
His department previously denied he played a part in the Christmas party on December 17 2020, instead saying he “walked through the team’s office on the way to his own office”.
The Prime Minister, accused of attending up to six of the events under question, received one of the legal quizzes last month.
The scandal has threatened his leadership, with multiple Tory MPs calling for his resignation and pressing for a vote of no confidence.
But the anger among Mr Johnson’s colleagues has cooled, for now at least, as he leads Britain’s response to the Russian invasion of Ukraine.
On Friday, a Cabinet Office spokesman said: “It would not be appropriate to comment on speculation.
“The Cabinet Secretary and the Prime Minister are fully focused on the vital work this Government is doing on the illegal invasion of Ukraine.”
