Legal action has been dropped against a 15-year-old who faced prosecution for branding Scientology a "cult".
The teenager held up a sign which read, "Scientology is not a religion, it is a dangerous cult", in May outside its headquarters in the City of London.
City of London Police said it had received complaints and warned the teenager to get rid of the sign as it breached the Public Order Act.
Human rights campaigners vowed to take action against the police.
Lawyers for the human rights group Liberty represented the teenager in his legal battle.
James Welch from the organisation said: "The police may have ended their inquiries into this tawdry incident but rest assured that Liberty's inquiry will continue.
"Democracy is all about clashing ideas and the police should protect peaceful protest, not stifle it."
The teenager's mother said the move was "a victory for free speech".
She said: "We're all incredibly proud of him.
"We advised him to take the placard down when we realised what was happening but he said 'No, it's my opinion and I have a right to express it'."
A Crown Prosecution Service (CPS) spokesman said: "In consultation with the City of London Police, we were asked whether the sign was abusive or insulting.
"Our advice is that it is not abusive or insulting and there is no offensiveness (as opposed to criticism), neither in the idea expressed nor in the mode of expression."
A spokeswoman for the City of London Police said: "The CPS review of the case includes advice on what action or behaviour at a demonstration might be considered to be 'threatening, abusive or insulting'.
"The force's policing of future demonstrations will reflect this advice."