Horticultural experts have compared it to finding a wondrous and unknown library of rare first editions, said the head gardener of Wentworth Woodhouse, Scott Jamieson, recalling the discovery of camellias believed to be some of the oldest and rarest in the western world. The important shrubs have been identified in a dilapidated glass and brick building on the estate of Wentworth Woodhouse, a spectacular Georgian palace near Rotherham in South Yorkshire, which is the subject of one of the UK’s biggest heritage restoration projects. The huge house and gardens are gradually revealing their secrets, one of the most eye-catching of which has been the discovery of the camellia house. “It is quite incredible,” said Jamieson, who has been at Wentworth Woodhouse for 17 years. “There are very few camellia houses left anywhere, certainly not one with a great collection of historic camellias.” For many years the building, with jagged glass likely to fall at any point, was too dangerous to go into. That glass roof has been removed, allowing access to the 200-year-old camellias. The shrubs were imported for wealthy families in the 18th century on merchant ships belonging to the East India Company. The camellias were, wrongly, judged so precious and fragile that they needed to be pampered in a building with lots of light and a stove to heat the brick walls. There are 19 camellia shrubs in total, with the oldest believed to have arrived in 1792. That makes it older than any in the nationally important camellia collection at Chiswick House in London and a contender to be the oldest anywhere in the west. With the help of Chiswick House and others, three varieties have been identified and the detective work continues to find out more. It was about two years ago that Jamieson began trying to work out what the building was. He sent a plaintive callout to people who might know and a number of experts came in and were amazed. “They said it was almost like having a library of first editions … it’s that important in gardening history. So it’s wonderful.” The survival of the camellia house is all the more remarkable given it spent decades only feet away from an open cast mine, which began operating in the 1940s. It was a lunar-like landscape, said Jamieson, who has recently led a project restoring the original pathways to the gardens. “It would have been a strange environment, I imagine, you would have had a hacking cough and stinging eyes with that amount of pollution in the air. And it would have been noisy.” Two hundred years ago it would have been a very different story, with the ladies gathering in the camellia house to drink tea, gamble and smoke when the men were out hunting. The plan now is to develop the site into a specialist tea house and a community cafe. It is hoped it will open in 2022. Wentworth Woodhouse remains one of the nation’s most spectacular stately homes most people have never heard of. To say that Wentworth Woodhouse is “over the top” is almost an understatement. It is twice as wide as Buckingham Palace, has 124,600 sq ft of living space, three acres of roofs, a room for every day of the year and is often described as Britain’s biggest house. The entire house would once have screamed opulence and excess, the walls lined with important paintings – notably George Stubbs’s Whistlejacket, now a star of the National Gallery. The volunteer guide Steve Ash says it hides in plain sight. “It’s lovely when you see young people come, because very often this is the first time they’ve been to a place like this. Then they realise it is on their doorstep. It is absolutely a proper hidden gem.” The property was in a terrible state when it was bought for £7m in 2016 by the Wentworth Woodhouse Preservation Trust – established after a campaign by a local business owner, Julie Kenny. It is now the subject of a restoration project that could easily cost more than £250m. The house was given £4.6m of levelling up money by the chancellor, Rishi Sunak, in his October budget. That money will enable work to begin this year on the house’s vast stable block, a building so grand that some people assume it’s the main house.