Kensington Palace has accused paparazzi photographers of harassing Prince George, saying the royal toddler had become their "number one target" and accusing them of going to "extreme lengths" to get pictures of him.
In an unusually strongly-worded open letter, Jason Knauf, the communications secretary of the Duke and Duchess of Cambridge, said the tactics used by some photographers were creating a "very real security risk".
Scotland Yard echoed complaints that covert photographers pose a security threat and warned they could be putting themselves at risk from armed intervention at a time when officers are at a "heightened level of readiness".
The palace's hard-hitting letter detailed a series of incidents involving paparazzi, such as using children to draw Prince George into view in playgrounds and an incident last week when a photographer set up a "hide" in his car with sheets and supplies of food and drink as he staked out a play area.
The actions of photographers had left William and Kate "concerned about their ability to provide a childhood for Prince George and Princess Charlotte that is free from harassment and surveillance".
Other incidents included:
:: photographers pursuing cars leaving family homes
:: surveillance of the Berkshire home of the duchess's parents, Carole and Michael Middleton
:: hiding in dunes to take photos of Prince George playing with his grandmother
:: hiding on private property in fields and woodland around the duke and duchess's home in Norfolk
In the letter, Mr Knauf said: "It is of course upsetting that such tactics - reminiscent as they are of past surveillance by groups intent on doing more than capturing images - are being deployed to profit from the image of a two-year-old boy.
"In a heightened security environment, such tactics are a risk to all involved.
"The worry is that it will not always be possible to quickly distinguish between someone taking photos and someone intending to do more immediate harm."
Meanwhile, Scotland Yard warned photographers that they face putting themselves in danger at a time when the national security threat level from international terrorism is severe.
A statement said: "The covert actions of photographers have at times caused concerns during police protection operations when they have been considered a possible security threat."
It continued: "Photographers are potentially putting themselves at risk from armed intervention where our armed officers perceive a risk to the personal safety of their principal, the public and themselves.
"When assessing potential threats, armed officers have to make split-second decisions regarding their use of force in order to protect their principals, the public and their colleagues.
"Whilst the majority of photographers work responsibly, we would ask those that choose to use covert tactics to consider their actions in light of this potential risk."