The investigation into whether Sir Keir Starmer broke coronavirus rules cost the public £101,000, police have said.
Durham Police launched an inquiry after the Labour leader was filmed drinking beer in an MP's office in April 2021 when Covid restrictions were in place.
Responding to a Freedom of Information (FOI) request, the force revealed nine officers spent about 3,200 hours on the so-called Beergate investigation.
Sir Keir and his team were cleared of any wrongdoing in July.
At the Durham gathering on 30 April, which was in the run-up to the Hartlepool by-election, people drank beer and ate curry in the constituency office of Labour City of Durham MP Mary Foy.
Social distancing rules - including a ban on indoor mixing between households - were in place at the time.
However, Labour had argued the food was consumed between work events, meaning the gathering was within the rules.
They had been initially cleared by police in February of breaking any laws but officers reopened the investigation into the event in May after receiving "significant new information".
Following the conclusion of that inquiry, police said they would not be issuing any fines and no further action would be taken.
The FOI revealed a detective superintendent, a detective inspector, a detective sergeant and six detective constables from the Major Crime Team worked on the case, alongside two members of police staff.
The request was submitted by National World, which first reported the story.
The force's reply said: "After careful consideration and performing a public interest test, I [the decision maker] have deemed that the public interest lies in the disclosure of this information, as it relates to the spending of public money, and also the resources Durham Constabulary had to utilise to conduct this investigation."
It said the money came from the "general policing budget" and that the Major Crime Team "continued to operate normally and conduct other investigations".
Earlier this year, then-Prime Minister Boris Johnson was fined for attending a birthday party during lockdown in June 2020.
Footage shows Sir Keir Starmer drinking beer with colleagues in Durham on 30 April 2021
WATCH: Keir Starmer's statement when he was cleared in July