Police will be taking no action over claims a voice coaching session for Sir Keir Starmer in December 2020 broke Covid lockdown rules.
A Met Police spokesperson said the alleged incident fell outside the three-year deadline for initiating proceedings related to pandemic-era legislation.
The Conservatives had called for an investigation into whether a meeting at Labour Party headquarters on Christmas Eve in 2020 broke the law.
Sir Keir, who has denied breaking lockdown rules, said he was working in his office at the time on his response to Boris Johnson’s Brexit deal.
Earlier, Downing Street said communication skills specialist Leonie Mellinger was “a core part of a small team” working with Sir Keir, then leader of the opposition, during the pandemic.
She is understood to have joined both Sir Keir and then-shadow chancellor Rachel Reeves to help him prepare for Covid statements and press conferences.
No 10 would not be drawn on how many times they met or how many people were present but said the prime minister believed it was not reasonably possible for Ms Mellinger to do her job from home, as she had done other occasions.
Sir Keir’s spokeswoman said it was “a hugely significant moment for the country and it was in line with the requirements that you could go to work if were you able to do so”.
She dismissed Tory criticism as “desperate mudslinging”.
Sir Keir hit back at Tory attacks over the meeting during Prime Minister’s Questions.
“In December 2020, I was in my office working on the expected Brexit deal,” he said.
“With my team we had to analyse the deal as it came in at speed, prepare and deliver a live statement at speed on one of the most important issues for our country in recent years.
“That’s what I was doing. What were they doing?
“Suitcases of food into Downing Street, partying and fighting, vomiting up the walls, leaving the cleaner to remove red wine stains. That’s the difference – I was working, they were partying.”
Several parties were held at Downing Street during Covid lockdowns, with more than 100 fines issued.
Sir Keir’s use of a voice coach was revealed in excepts of Get In, a book about his leadership being serialised by the Times newspapers.
The Tories seized on the story to suggest it amounted to evidence of a potential breach of lockdown rules.
Ahead of Christmas in 2020, London and south-east England were put under Tier 4 lockdown rules, with people banned from mixing indoors.
However, there were some exemptions, with people able to leave their home and meet others if this was “reasonably necessary” for work.
A spokesman for Conservative leader Kemi Badenoch said: “The key question here is: is a voice coach a key worker who can travel from Tier 4 to Tier 3 during lockdown?
“It doesn’t matter if you’re part of a core team, that is the question. Now, Keir Starmer said that lawmakers can’t be lawbreakers. It is almost unimaginable to disagree that that was a clear breach of the Covid rules.”
He added that he was accusing Ms Mellinger of breaking the law, rather than Sir Keir, but claimed the comment about lawmakers not being lawbreakers applied to the Prime Minister “by proxy”.
When asked by journalists on Monday, the PM denied breaking Covid rules.
Ms Mellinger has been approached for comment.
A Met Police spokesperson said: “We can confirm we have received a report.
“The specific legislation that would be used by police forces dealing with alleged offences during Covid has a three-year deadline for initiating proceedings.
“As this alleged incident falls outside of this timeframe, no action will be taken.”
