An oil painting which was repeatedly used as a dartboard and slashed with a knife while it hung for years on the walls of a youth detention centre in Buckinghamshire was today unveiled on the walls of the National Gallery in London and declared an important work of art.

The picture was in an extremely sorry state, pock-marked with pin-pricks and severe gashes, when the local council finally removed it from the Denham Court centre for delinquent youths in the 1980s when it decided to sell the building.

Having been relegated to a storeroom after years of abuse, it has now been identified as a 17th-century depiction of the ostentatious house which Rubens, the Flemish master and a celebrated and wealthy painter of his day, built for himself in Antwerp.

Susan Foister, director of collections at the National Gallery, described Courtyard at the Rubenhuis as “really significant” because it gives a dramatic new insight into how the historic house - which is now open to the public - looked originally.

Thought to have been painted between 1645 and 1675, it is now the earliest depiction of the famous building. It shows, for example, a frieze on the façade - perhaps painted by Rubens himself - of which scholars had been unaware. The frieze does not feature on a 1680s engraving which was until now the earliest image.

A group of figures seen emerging from the building are thought to represent Rubens, his wife and their young son and relates to a famous image in the Metropolitan Museum in New York.

Before being turned into a centre for wayward youths, Denham Court had seen better days as a 17th-century stately home in Buckinghamshire. It is now a golf-club.

The painting is believed to have been acquired by one of the house's 19th-century owners, Thomas Hamlet, who also had an important Titian, the Bacchus and Adriadne, now in the National Gallery, in his collection.

The Rubens House painting was removed after the council, which had acquired Denham Court in the 1930s, decided to sell the building. Nine other paintings there had also suffered extensive damage by the less than appreciative youths.

Although the damage made by the youths was filled in and retouched by a restorer, the painting had been relegated in subsequent years to storerooms in the village of Halton, near Aylesbury. Some 95 per cent of the council's 5,000 works are in storage.

It was there that Anne Cowe, one of twenty-five researchers despatched around the country to create the first national database of paintings in Britain's public collections, came across it.

From this week, it goes on show to the public in an exhibition, “Discoveries: New Research into British Collections”, that celebrates the National Inventory Research Programme (NIRP), a research project based at the University of Glasgow, with Birkbeck College (University of London) and the National Gallery as partners.

As some regional museums can no longer afford to employ staff to research their collections, researchers were sent in 2004 to 200 regional museums to shed new light on European paintings from 1200 to 1900 – uncovering a variety of stories, interpreting symbolism, suggesting attributions and enhancing understanding of a wide range of pictures.

The project has enabled museums and galleries to research and catalogue their collections - in some cases for the first time.

Yesterday, about 8,000 European oil paintings were launched online, providing all the research uncovered over the past three years in the first national database of what is in every museum in the country.

Further research will be conducted on the Rubens House painting, but it is thought to have been painted by Anton Günther Gheringh, an architectural artist.

On why it had been overlooked for so long, Xanthe Brooke, the curator of European art at the Walker Art Gallery in Liverpool and a member of the steering committee for the NIRP, said: “How many art historians visit detention centres?”

“Discoveries” runs from tomorrow until February 10.

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