Sir Keir Starmer and Angela Rayner have received questionnaires from Durham Police as the force investigates a rally held at party offices during lockdown.
The Labor leader and his deputy said they would step down if fined by police.
Sir Keir was filmed drinking a beer in an MP’s office after a day of campaigning for local elections in Durham in April 2021.
Ms Rayner was also present at the event, dubbed by some “beergate” following Downing Street’s “partygate” investigation into lockdown breaches.
At the time of the Durham rally, non-essential retail and outdoor venues, including pub gardens, were open, but social distancing rules – which included a ban on mixing households indoors – are remained in place.
But Labor argued the food was eaten between work events, meaning it was within the rules.
Earlier this month, Durham Constabulary announced it had reversed an earlier ruling that no offense had been committed, after receiving ‘significant new information’.
Sir Keir has previously said he was ‘putting everything on the line’ promising to quit if he was handed a fixed fine, and that quitting would be ‘the right thing to do’.
On Tuesday, a Labor Party spokesman said: ‘Keir Starmer and Angela Rayner have received questionnaires from Durham Constabulary.
Labor has sought to contrast Sir Keir’s actions with those of Boris Johnson, who refused to quit after being fined by Met Police for a rally at No 10 in June 2020 to mark his 56th birthday .
Union sources are confident they can prove the Durham event was work-related and those in attendance were taking a break to eat while working late on preparations for the Hartlepool by-election.