A union boss who used a megaphone close to two police officers' ears has been found not guilty of assaulting them.
There was no evidence taxi union chief James Farrar had committed a crime, Judge Philip Bartle QC said.
PC Ann Spinks had told Mr Farrar's trial she was left with ringing in her ear "like a fire alarm going off" after a megaphone was purposely aimed at her.
Mr Farrar, 51, said the legal action against him was "a corrupt and crude attempt... to break our union".
The chairman of the United Private Drivers' branch of the IWGB union said the Metropolitan Police and Transport for London (TfL) had also tried to "further disenfranchise precarious workers" and he had instructed his lawyers to "pursue the matter".
At Southwark Crown Court, Judge Bartle instructed the jury to find Mr Farrar not guilty of the two counts of assault he faced.
Dismissing jurors, the judge said: "The facts did not justify the offence in either case of assault by beating because the offence requires unlawful application of force."
Ear 'hot to touch'
The confrontation happened at a demonstration in Parliament Square, which the court heard was organised by Mr Farrar, against TfL plans to exempt black cabs from the congestion charge but enforce it for Uber and minicab drivers.
Mr Farrar, from Bordon, Hampshire, had been told not to use the megaphone at ear level before the alleged assault, his trial heard.
PC Spinks told the jury the union boss had continued shouting through his megaphone, which was about a foot away from her head.
She said she told another officer at the time: "[Mr Farrar] had blasted the megaphone into my left ear causing ringing, tinnitus, like a fire alarm going off in your ear."
"My ear at that time had gone bright red and was quite hot to touch," she added.
Although no physical beating took place, the prosecution alleged Mr Farrar's actions amounted to an "unlawful application of force".
Neither police officer suffered lasting hearing loss as a result, the court was told.