The Labour leader has been under growing pressure after Durham Police announced last Friday that it was re-investigating claims that he may have broken the regulations during a beer and curry gathering while on the road campaigning with Labour colleagues in Durham last April.
Conservative ministers have lined up to accuse the Labour leader of hypocrisy after Sir Keir called for Boris Johnson and Rishi Sunak to resign for being fined for attending a gathering in Downing Street in June 2020, while lockdown laws were in place.
Labour did not immediately respond to a request for comment about the story but in a live internet with the national press, Sir Keir is to say he will step down if he is issued with a fixed penalty notice over the gathering.
With Downing Street braced for more fines in the coming days, it is seen by allies as an attempt to wrest back the initiative and keep the pressure on Mr Johnson who has repeatedly refused calls to resign over the partygate affair.
The Prime Minister has already confirmed that he has received one fine for attending a ‘surprise’ birthday party in Downing Street in June 2020.