For viewers of a certain age it is instantly recognisable. Botallack Manor, on the Penwith peninsula in western Cornwall, doubled as Nampara, the home of Ross Poldark and his family, in the original 1970s Poldark television series.

Today, the Grade II-listed house, built in the 17th century and boasting spectacular views of the Tin Coast, remains a magnet for Poldark fans, many drawn to this wild and remote location by the latest BBC adaptation of Winston Graham’s novels.

But while Poldark has enjoyed a new lease of life, the same cannot be said for the house. For the past five years it has lain empty and in an increasing state of neglect, so much so that it has been included in the latest (30th) edition of the buildings at risk catalogue produced by campaign group Save Britain’s Heritage.

Its latest catalogue lists more than 100 forgotten buildings that Save believes represent an unused resource and a rich repository of the nation’s history.

“Without a clear and determined focus, we stand to lose many buildings that tell the story of Britain and give places their distinctive character,” said Liz Fuller, Save’s building at risk officer. “For 30 years, Save’s buildings at risk catalogues have been highlighting just what is at stake if a conscious national effort is not made to prevent neglect and actively to incentivise the repurposing of disused historic buildings.”

Botallack Manor is to be renovated but other historic buildings have disappeared through disuse and neglect. Photograph: Christopher Barnard/Alamy

The good news for Botallack Manor is that its owner, the Tregothnan Estate, has pledged to take action. A spokeswoman for the estate told the Observer that the building will be leased out as a farmhouse following a two-year renovation already under way.

But many of the other properties on the Save list may not end up enjoying such a rosy future. Liverpool’s Everton Library, built in 1896 with a striking octagonal tower, has been the subject of many redevelopment proposals that have come to nothing.

The Iron Duke, an art deco public house in Great Yarmouth, was completed in 1948 and granted Grade II status in 2017, in recognition of its architectural interest and historic importance, but remains under threat of demolition.

Robin Ellis as Ross and Angharad Rees as Demelza in the 1970s series of Poldark. Photograph: BBC Photo Library

Cliff House School is described by Save as “a fine Grade II-listed Leeds building … built in 1846 in a restrained classical style by Joseph Cliff, a prominent local business man … and is in real need of a new use to bring it back to health and useful life.”Without a clear and determined focus, we stand to lose many buildings that tell the story of Britain and give places their distinctive character,” said Liz Fuller. “For 30 years, Save’s buildings at risk catalogues have been highlighting just what is at stake if a conscious national effort is not made to prevent neglect and actively to incentivise the repurposing of Britain’s disused historic buildings.”

The buildings included in Save’s catalogues over the past three decades tell a story of British society in flux. Many are municipal buildings such as courts and town halls that now stand empty after new alternatives were built and services consolidated. Pubs and cinemas also feature heavily, as do schools.

Fuller said: “We still have a good helping of rural buildings that would make amazing accommodation and need to find saviours. We also have buildings in deprived areas which could be a focus for regeneration if the right use could be found, and enough funding to get a project started.”

The annual publication of the catalogue and the construction of an online database of all buildings at risk around the country has helped raise public awareness of the country’s neglected gems. Some have gone on to be transformed by members of the public who have caught the renovation bug, made popular by television shows such as Grand Designs and The Restoration Man.

Fuller cited the restoration of a Cumbrian farmhouse which appeared in the 2009 catalogue, and a manor house in Wiltshire featured in 1992 and 1994, as two notable success stories.

The latter, she said, was spotted by someone who had no experience at all of restoring houses but a great desire to bring somewhere beautiful back to life. “The restored house is an absolute beauty,” she added.

The Iron Duke pub in Great Yarmouth. Photograph: Caroline Jones

But some buildings are lost forever. Save says it campaigned in vain to protect the Futurist Cinema – an early 19th-century building in modern baroque style in central Liverpool. The unlisted cinema stood in a conservation area and was in the buffer zone of Liverpool’s Unesco-listed “maritime mercantile city”, but it was demolished in 2016.

Empty buildings are also vulnerable to other threats, notably fire. Two weeks ago a derelict Fison’s fertiliser factory in Bramford, Suffolk, which had been on Save’s register for the past couple of years, was devastated by fire, resulting in what Fuller described as “a very significant and tragic loss”. Griff Rhys Jones, president of the Victorian Society, described the building, constructed in the mid-19th century, as “irreplaceable”.