A £1m burglary at an East Sussex country mansion was a "highly-planned" operation, police have said.
Detectives made a fresh appeal for information about the burglary at Firle Place on the BBC's Crimewatch Roadshow programme on Wednesday.
Rare 18th Century Sevres porcelain was taken in the theft at the Lewes estate, which has been used to film TV shows including Jonathan Creek.
Police said the theft last July was not the work of an opportunist burglar.
Det Ch Insp Mike Ashcroft said: "The methods used to avoid detection by the security measures within the building showed planning and experience by those responsible."
He said Sussex officers were working with other agencies and forces to find the offenders and recover the stolen property.
He added: "Some of the stolen items have been at Firle Place for hundreds of years and this crime has denied visitors the enjoyment of sharing in this part of its history."
A pair of identical vases made in 1763 and a Hollandaise Nouveau vase were among items stolen.
The estate has been the home of the Gage family for more than 500 years and is used as a film and TV location.
The house is open to the public, and Lord Gage has previously said the burglary would prevent members of the public from viewing the historic porcelain collection.