Former PC Matthew Thomas, who served as part of the Met's Parliamentary and Diplomatic Protection service (PaDP), tested positive for the illegal drug while at work.
Detectives suspected he was taking illicit substances when his phone number was found in a mobile confiscated from a suspected drug dealer.
A test was administered on April 23, while PC Thomas was at work.
The urine sample showed that he had consumed cocaine within the previous 72 hours and “was at least ten times over the cut off level required to indicate a positive test result”, the misconduct hearing heard.
“Thomas, an officer who carries a firearm, was on duty at the time the test was taken, and therefore this was the level of drugs present in his system while on duty,” Chair of the disciplinary panel, Assistant Commissioner Barbara Gray said.
“There is no plausible explanation for the presence of cocaine in Thomas’ system, other than the fact that he knowingly took the drug.
She added: “Thomas…put those that rely on him for protection, members of the public, diplomats and members of government, colleagues and himself at risk. He can have been in no doubt that the use of cocaine was unacceptable behaviour.
The Assistant Commissioner said it was “also significant” that Thomas “was identified as a potential drug user” through a “suspected drugs line”.
The Directorate of Professional Standards told Thomas he had tested positive for cocaine on May 3, 2023.
But he remained an officer until he resigned on September 25, with his last day of service on October 12.
At an accelerated misconduct hearing last week he was found to have committed gross miscoduct with a “breach of the Standards of Professional Behaviour so serious that dismissal would be justified”.
This backlog is a “significant increase” on last year and the force has said it wants 30 hearings to take place per month as it attempts to weed out unfit officers from its ranks.
Met Commissioner Sir Mark Rowley has vowed to rebuild public trust and confidence in the force after it was shattered by a slew of scandals, including the murder of Sarah Everard by serving officer Wayne Couzens and the unmasking of former PC David Carrick as a serial abuser and rapist.