Letters warning the media against "acts of harassment" on the Duke and Duchess of Cambridge at their Norfolk home have been distributed by police, according to reports.
Kate and William left London for Anmer Hall, on the Queen's private Sandringham estate, with their new baby Princess Charlotte and her elder brother Prince George yesterday.
The BBC said Norfolk Police had given the media letters stating that while the Cambridges are in residence they have "a more than reasonable expectation of privacy".
The letter, signed by the couple's communications secretary, called for "acts of harassment and breaches of privacy to cease".
It said: "There have in the past been a number of intrusions into the privacy of the Royal Family which in the main have been as a result of professional photographers using long-distance lenses, not only to observe the Royal Family, but also to photograph them going about their activities on the estate."
Previous warnings to photographers meant "the position has greatly improved".
But it continued: "However, we would remind you again of the position. The Sandringham Estate trusts that there will not be a need to take any further action other than bringing these points to your attention."
The Duke and Duchess will spend the first few weeks of Charlotte's life in their refurbished Georgian mansion as they get to grips with looking after both a newborn and a toddler.
William is on two weeks' paternity leave from his job as an air ambulance helicopter pilot, and is expected to start the final phase of his training at the beginning of June.