The home of Sir Reginald Sheffield – the father of Samantha Cameron – is believed to be one of those targeted by the gangs. And, in the most serious in the wave of thefts, porcelain antiques worth around £500,000 were stolen from Firle Place in Sussex.
The former head of Scotland Yard's arts and antiques unit, Dick Ellis, said that gangs were using the internet to find out what items were on view in which stately homes and then using online auction sites to sell the goods. "They are taking advantage of the goodwill of these people, many of whom open their homes to the public," he said.
Mr Ellis added: "It is not a case of closing the attractions but owners need to increase security. They need high-quality CCTV and motion and acoustic sensors on the windows because they are dealing with sophisticated methods of breaking and entering."
Mr Ellis estimates that three highly professional gangs are responsible for at least 21 major burglaries and 15 attempted burglaries in the past three years. Mystery still surrounds the raids, from which few items have ever been recovered. It is unclear why the thieves would target porcelain artworks, which are relatively difficult to move without damaging, as Mr Ellis said: "Few burglars carry bubble-wrap."
Firle Place, owned by the family of a London art dealer, was burgled last July by thieves who used a ladder to break into the 18th century mansion at night. They climbed through a window and broke into two display cases, making off with a 1743 Meissen statue by Johann Joachim Kändler, The Indiscreet Harlequin, and a rare Sèvres Hollandois Nouveau vase, made in 1761, as well as 18 works, none of which have been recovered.
Among the other houses to be targeted are Sutton Park, near York, Longner Hall in Shrewsbury and Castle Howard in North Yorkshire, all of which are open to the public.
At least £20,000 worth of porcelain items were stolen from the Georgian Sutton Park, owned by Mrs Cameron's family since 1963. Thieves took a Meissen teapot shaped like a monkey – said to have been in the family for two centuries – and a 19th-century bronze bust of an Asian woman by Charles Cordier, The Art Newspaper reported.
It is thought that the burglars spent less than a minute in the house during the May 2009 raid and had already identified the items they were to steal. The house had also been the subject of an attempted burglary earlier that year. A 28-piece Worcester dessert service was taken during the raid on Longner Hall last August.
Mr Ellis said he believed that the thefts were the work of three gangs: one which targeted houses at night, removing sections from windows; another which typically forced a door or window open, creating a gap through which a small gang-member squeezed; and one which targeted country houses open to visitors.
He added that he felt that, since few of the pieces have been recovered, the thieves had shipped their loot to Europe, where Meissen and Sèvres are highly collectable.
"Instead of laying the haul down, and gradually feeding it down into the market, the recent trend is instant disposal," said Mr Ellis.
There have been few arrests linked to the thefts. Mr Ellis, who works with the Art Management Group – which helps those seeking to buy or recover art and antiques – blamed that lack of success on Britain's police forces being "run on a county basis".
"No force has an overview of similar crimes occurring elsewhere, so investigations are limited and local. Little progress has been made in tackling this surge in porcelain thefts," added Mr Ellis, whose work was commissioned by the Ecclesiastical Insurance Group.
He was also at a loss to explain why the thieves would begin targeting porcelain, the market for which has remained stable.
Stately homes under siege
Firle Place, East Sussex
The seat of Lord Gage was raided in 2009 and a haul of items worth between £500,000 and £1m stolen. None of the 20 works have ever been recovered. The house has been burgled on two other occasions. In 2001 two antique tables worth more than £10,000 were taken during an open day, and in 2004 antiques worth £100,000 were stolen. Perhaps surprisingly, the house remains open to the public.
Sutton Park, North Yorkshire
Owned by David Cameron's father-in-law, it was looted in 2009. Thieves took a £20,000 Meissen teapot in the form of a monkey, and a 19th-century bronze bust of an Asian woman by Charles Cordier. The house has been in Samantha Cameron's family since 1963. The house, which has award-winning gardens and tearooms, is available for hire and occasionally opens to the public.
Castle Howard, North Yorkshire
The backdrop for numerous films, including the 2008 adaptation of Evelyn Waugh's Brideshead Revisited, Peter Ustinov's Lady L and Stanley Kubrick's Barry Lyndon, it was also the subject of an attempted robbery by Andrew Shannon, an Irishman who stole antiques and paintings from six English stately homes on a "long weekend of crime" in 2009. Shannon was jailed for three years after his attempted theft was foiled by a Castle Howard caretaker during a visit to the attraction.
Longner Hall, Shropshire
Longner Hall, designed for the Burton family by John Nash in 1803, was burgled last year. The thieves made off with a 28-piece Worcester dessert service. The house remains open to the public.
Penshurst Place, Kent
The ancestral home of the Sidney family, whose most illustrious member was the Elizabethan soldier-poet Sir Philip Sidney, was burgled despite its current owner, Viscount De L'Isle, previously having decided to nail the house's tapestries to the walls. It is still open to the public.
