Leading British historians are calling for the return of a huge hoard of UK art treasures that has gone missing in the United States.

The works – a slice of the nation’s cultural history – range from ship-loads of paintings and sculptures to entire interiors from old houses, transported across the Atlantic as part of the largest movement of art and architecture since the Renaissance. The former V&A director, Sir Roy Strong, is one of the academics calling for Britain’s vanished heritage to be found.

The extent of the lost art and architecture has emerged since the launch in January of an appeal to find a Tudor oak parlour “missing” from Gwydir castle in north Wales. The ornate panelling and a fireplace were bought by the US billionaire William Randolph Hearst in the 1920s and were last seen at his palatial home in New York in the 1930s.

Efforts to find the room, one of two from the castle sold to Hearst, have so far failed. But the search has brought to light the greatest single loss of cultural artefacts from Britain. Though many pieces shipped across the Atlantic passed into public collections in the US, and some worldwide, the fate of the bulk of the material is unknown.

Hearst, fictionalised by Orson Welles in the film Citizen Kane, was an obsessive collector of European – especially British – art and architecture. He was dubbed “the great accumulator” by one dealer. Rumours persist that sealed Hearst containers remain in storage.

Gwydir Castle’s missing Tudor oak parlour. Photograph: Gwydir Castle's 1921 sale catalogue

The largest Hearst storage site is in the Bronx, New York, but other warehouses are believed to exist across the country. His fantasy medieval castle at San Simeon, California – Xanadu in the film – displays many works, though they are thought to be only around 10% of his entire collection. More than 90 rail wagons brought treasures to San Simeon, and one of the final scenes in Citizen Kane shows an endless vista of crated art at Xanadu.

Hearst was one of several super-rich Americans vying to amass art and antiques. John D Rockefeller, JP Morgan and Henry Clay Frick were also major players, with an extensive “second tier” of buyers below them.

For nearly 60 years, from the 1880s, items from Italy, France, Spain, Germany and Greece were snapped up, but Britain was the richest source. The trade was frenzied. When the Titanic sank in 1912, 30 tons of crated English architectural objects were on board. Entire historic interiors would be acquired – panelling, fireplaces, doors, paintings, timbers and plaster ceilings, libraries and tapestries – and shipped as job lots, often without an inventory. Artworks in particular were sold “en bloc” – by quantity – by dealers with no detailed description.

Over time, US galleries and museums came to own some of the items. Georgian rooms bought by Hearst, taken from Sutton Scarsdale Hall in Derbyshire, were used as film sets in Hollywood before ending up at the Huntington Library collection, California. Other Sutton Scarsdale rooms are held by the Philadelphia Museum of Art.

In the 1990s, the owners of Gwydir traced one of the castle’s two missing interiors, a 1640s room, to the Metropolitan Museum of Art in New York, which acquired it from Hearst. The room had been stored at the museum for decades, and the owners bought and reinstated it.

The gothic-style dining room at Hearst Castle. Photograph: Alamy Stock Photo

The extent of exports of British art and antiques to America is known to a few academics, but Gwydir’s search for its lost room has brought this episode out of the shadows. Now calling for a concerted effort to find the lost heritage are the pre-eminent historians Sir Roy Strong and John Harris.

Strong told the Observer: “There were ship-loads of early English portraits exported, not just grand things. There were interesting Elizabethan and other pictures. Back then, you wouldn’t have got 50 quid for an Elizabethan painting.

“It was the fashion, the English ‘Tudorbethan’. There’s English sculpture – how much of that went to America? We don’t know. There were no export controls. Records just went over to America, those of fantastic gardens, for instance. The fate of the rooms has never been highlighted.

“A large proportion of Britain’s art history from the 16th to 18th centuries may be missing.”

John Harris, who, with Marcus Binney – founder of SAVE Britain’s Heritage – campaigned in the 1970s to prevent heritage neglect, shares Strong’s concern. Harris is the only historian to have studied the export of artefacts from the UK. “I lived in New York in the early 1960s,” Harris told the Observer. “Around 20 houses on Park Avenue alone had old English rooms. Hundreds, if not in the low thousands, of items [are unaccounted for]. Some of the finest craftsmanship. At least 200 rooms were taken apart.

“We have underestimated the number of [historic] rooms in the US. It is unclear what is in storage, what the Hearst people have. It is odd that there has never been an effort to identify what is in the States.”

The billionaire publisher William Randolph Hearst was an avid collector. Photograph: Bettmann Archive

The scale of the buying was historic. “Only the Renaissance princes were spending on an equivalent scale,” says Dr Mark Westgarth, art historian at Leeds University and a specialist in the art trade. “One of the reasons why heritage laws began in Britain was to stop the flood of material to America.

“Hearst was notorious for buying pieces then leaving them in storage.”

By the late 1930s, Hearst’s empire faced bankruptcy and, in 1941, 20,000 lots were auctioned off at New York department stores Gimbels and Saks. “There hasn’t been sufficient awareness of this aspect of what has been exported to America,” says Harris. “That was seriously to this country’s loss.

“A lot of the documentary records have vanished, dealers’ papers especially. Years ago, I searched the records of one, French & Company, and Hearst without success. I’ve always been told there are Hearst stores in the US, difficult to access. Efforts must be made to examine Hearst sites and open containers. But I’m past it now.”

Those looking after the surviving Hearst archives believe there is much to be discovered. “The whereabouts of a lot of the items Hearst bought are not known,” says Dr Catherine Larkin of the William Randolph Hearst Archive at Long Island University, New York.

“Things have gone missing by being placed in homes which might not exist any more, or are still in one of Hearst’s many warehouses.”