Sir Keir Starmer is to be investigated by police amid allegations he broke lockdown rules last year following receipt of “significant new information”, Durham Constabulary said.
The Labour leader has come under pressure since footage emerged of him drinking a beer with colleagues in April 2021 in Durham during campaigning for the Hartlepool by-election.
This week, Starmer said he wanted to focus on the cost-of-living crisis and not Conservative “mudslinging”.
At the time of the alleged gathering, non-essential retail and outdoor venues including pub gardens were open but social distancing rules, which included a ban on indoor mixing between households, remained in place.
A police statement on Friday afternoon said: “Earlier this year, Durham Constabulary carried out an assessment as to whether Covid-19 regulations had been breached at a gathering in Durham City on April 30, 2021.
“At that time, it was concluded that no offence had been established and therefore no further action would be taken.
“Following the receipt of significant new information over recent days, Durham Constabulary has reviewed that position and now, following the conclusion of the pre-election period, we can confirm that an investigation into potential breaches of Covid-19 regulations relating to this gathering is now being conducted.”
Police previously said they did not believe “an offence has been established in relation to the legislation and guidance in place at that time and will therefore take no further action in relation to this matter”.
A spokesman this month said they had “received a number of recent communications on this subject, which we are considering and will respond in due course”.
Prime Minister Boris Johnson, his wife Carrie Johnson, and Chancellor Rishi Sunak are among those to have already been fined for breaking Covid laws.