Boris Johnson has called on newspaper editors to rally behind the Spectator magazine in opposing the Royal Charter governing Britain's new system of press regulation.
The Queen approved the Royal Charter last month, which is backed by the three main parties and establishes a body to oversee the country's new press regulator.
Speaking at the magazine's Parliamentarian of the Year Awards, the London Mayor said: "Our ruling parties are daily purged and disinfected by a free press.
"I urge all editors to follow the Spectator's lead in rejecting the Royal Charter and tell the Privy Council to stick its charter in the privy!"
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This came after the Privy Council rejected a last-ditch legal challenge by the industry to stop the charter coming into force.
Johnson also took time to praise the Spectator's publisher, BBC presenter Andrew Neil, on "being the world leader of digital penetration".