The police watchdog has been urged to investigate Scotland Yard’s handling of the partygate investigation after pictures emerged of Boris Johnson apparently drinking wine at a lockdown-busting event for which he was not fined.

       Liberal Democrat deputy leader Daisy Cooper has written to the Independent Office for Police Conduct (IOPC) calling for them to examine the Met’s Operation Hillman inquiry into events in No 10 and Whitehall.

       Mr Johnson received a fixed-penalty notice (FPN) over a birthday party in the Cabinet Room in June 2020 but was told he would face no further action over other gatherings covered by the Metropolitan Police’s Operation Hillman inquiry.

       Those included the November 13 2020 gathering to mark former spin doctor Lee Cain’s departure from No 10, an event at which pictures obtained by ITV apparently showed Mr Johnson raising a toast and drinking wine.

       Prime Minister Boris Johnson (Henry Nicholls/PA)

       (PA Wire)

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       The Met has issued 126 FPNs to 83 people at events in Downing Street and Whitehall, including on November 13 2020, although the force has not said whether fines were specifically issued for Mr Cain’s leaving drinks.

       The Metropolitan Police declined to explain why the Prime Minister was not fined over the leaving party.

       Ms Cooper said: “The Met Police need to explain why Boris Johnson wasn’t fined for this event, despite being pictured in an apparent breach of the rules.

       “If anyone else had been pictured at a party like this during lockdown, surely this would have been enough evidence for them to be fined.

       “It does seem that there has been one rule for the Prime Minister and another for everyone else.

       “The complete lack of transparency in this investigation risks doing huge damage to public trust.

       “We need urgent clarity from the Met over why Boris Johnson wasn’t fined when others were.

       “If the Met won’t set out the basis on which they made their decisions, then it’s absolutely right that they should face an investigation.”

       The IOPC is unlikely to agree to her request as most complaints should be directed to the force responsible, with the watchdog usually only considering the most serious cases, such as those involving a death or serious injury following contact with the police

       Ms Cooper’s request could also be ineligible because complaints can only be made by someone who has directly witnessed an incident or is directly affected by it.

       But the Met’s decision-making process has also been questioned by lawyers, with the Good Law Project’s Jolyon Maugham suggesting he would take legal action.

       “We have now had advice from our QC and junior,” he said.

       “We will be sending a further judicial review pre-action protocol letter to the Met in relation to the apparent failures in its investigation into the Prime Minister later this week.”

       Barrister Adam Wagner, author of a forthcoming book on the coronavirus laws, said that at the time of the November 13 event “it was illegal to ‘participate’ in a gathering if that gathering was not reasonably necessary for work”.

       “Others got FPNs for this gathering so assume police considered it was illegal Why not the PM?”

       He added it is “impossible to understand how attending, raising a glass and making a speech wouldn’t be ‘participating'”.

       A spokesman for London mayor Sadiq Khan said the final report of Sue Gray – the senior civil servant investigating lockdown violations in Whitehall – must be published in full.

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       “The mayor has always been clear that nobody is above the law and that those who broke the rules, at a time the public were being asked to make huge sacrifices, must be held accountable for their actions,” the spokesman said.

       “The mayor understands why Londoners are seeking clarity given these latest revelations. The details of the investigation are a matter for the Met Police and it would be wrong for the mayor – who oversees the Met as police and crime commissioner for London – to intervene in an inquiry investigating his political opponents.”