Boris Johnson has refused to say whether he will resign if he is fined by police over the Partygate saga.
The Prime Minister is expected to be among some 50 people quizzed by Scotland Yard over rule-breaking gatherings in Downing Street and Whitehall during the pandemic.
The Metropolitan Police are sending out legal questionnaires in the coming days - and those involved could be slapped with fines.
Mr Johnson is believed to have attended six of the 12 gatherings police are investigating, including a BYOB bash in the Downing Street garden and an alleged party in his No11 flat.
No 10 said the PM has not yet been contacted by police, but added: "We would look to confirm contact of this sort as relates to the Prime Minister given the significant public interest."
Barrister Adam Wagner suggested the PM could be in line for £10,000 in fines if he is found to have broken the rules.
Officers are reviewing whether to add a Downing Street Christmas quiz to their inquiry after the Mirror published a bombshell picture showing the Prime Minister and officials and an open bottle of bubbly.
Mr Johnson was pressed on the row at a press conference in Brussels as he sought to shift attention to his diplomatic attempts to prevent war with Ukraine.
Asked if he would resign if he received a fine, he said: "That process must be completed and I'm looking forward to it being completed and that's the time to say more on that."
Pressed a second time, Mr Johnson responded: "I understand but we're going to wait for the process to be completed."
It comes as Tory former PM Sir John Major criticised the "brazen excuses" about the events in Downing Street and said Mr Johnson must go if he deliberately lied to Parliament.
In a speech at the Institute for Government, Sir John said "deliberate lies to Parliament have been fatal to political careers" and "must always be so".
"At No 10, the Prime Minister and officials broke lockdown laws," he said.
"Brazen excuses were dreamed up. Day after day the public was asked to believe the unbelievable. Ministers were sent out to defend the indefensible - making themselves look gullible or foolish.
"Collectively, this has made the Government look distinctly shifty, which has consequences that go far beyond political unpopularity. No Government can function properly if its every word is treated with suspicion."
Sir John, a longstanding critic of Mr Johnson, said trust in politics has hit a "low ebb, eroded by foolish behaviour" while "too often, ministers have been evasive, and the truth has been optional".
Angry Tory MPs are considering whether to call for a vote of no-confidence in the Prime Minister, with many waiting to see if he is fined, or further damaging details emerge from the Sue Gray inquiry.
Defence Secretary Ben Wallace admitted more damaging photos of events could be leaked in the coming days.
"Yes, there could be a photograph tomorrow, the next day or the day after - that's clearly what's behind some of the people's motives," he told Times Radio.
Whitehall enforcer Sue Gray revealed the police are investigating 12 events at No 10 and Whitehall during the pandemic for possible breaches of Covid rules.
Operation Hillman officers examining more than 500 documents and 300 images for their inquiry.
