Met chief Sir Mark Rowley said his force received serious and reliable intelligence that anti-monarchists would use rape alarms and loudhailers to terrify horses.
There is growing anger among a section of Tory MPs over the introduction of the Public Order Act, which gave police more powers to prevent disruption in the lead-up to the Coronation.
Prince William, the Prince of Wales, is the eldest son of King Charles III and Princess Diana. Palace insiders claimed William and Charles have gotten closer following Prince Harry's exit.