England’s National Gallery has bought a pair of stunning 18th-century French seascapes, once owned by Clive of India, for $6.4 million. But it has agreed to let the paintings hang in the home of one of America’s wealthiest industrialists until his death.

The groundbreaking deal is an ingenious, if slow-burning, solution to a double impasse.

David H. Koch, a socially well-connected petrochemicals tycoon and former playboy who owns Jacqueline Kennedy Onassis’s former apartment on Fifth Avenue, bought the paintings by Claude-Joseph Vernet for $6.4 million at an auction in London last year. But the British government stopped him from exporting them to America.

The National Gallery says that the pictures – “Calme” and “Tempete” – are of “outstanding aesthetic significance” and it was desperate to get them, not least because of the connection with Lord Clive, the conqueror of Bengal, who bought them from Vernet himself in 1773.

However, being starved of public funds for acquisitions, the gallery was unable to make the American an offer. Instead, Mr. Koch has agreed to give the Vernets away – but later.

In a complex deal, Mr. Koch – whose wealth was estimated at $2.2 billion six years ago – gave $6.4 million to the American Friends of the National Gallery. The charity has given a similar sized grant to the gallery in order to buy the paintings from Mr. Koch. But they will be lent back to him for his lifetime, and the government has waived normal rules and granted temporary licenses for the paintings to be exported to America.

Vernet, born in 1714, was renowned for pairs of paintings showing contrasting states of nature. Most of his pairs have been sold abroad individually, and “Calme: A Landscape at Sunset with Fishermen Returning With Their Catch” and “Tempete: A Shipwreck in Stormy Seas,” both painted the year Clive bought them, will become the only pair in a public British collection. They were sold by descendants of Clive.

Mr. Koch, who is in his mid-60s, is one of four brothers who inherited Koch Industries, an oil and gas refining company that grew into America’s second largest private company.

His twin brother, Bill, spent $65 million to win the America’s Cup in 1992, and David and his Southern belle wife, Julia, 25 years his junior, were called New York’s newest glittering couple when they bought Onassis’s 15-room apartment overlooking the Metropolitan Museum in 1998.

Government cutbacks to acquisition funds have made it virtually impossible for British collections to buy works on the open market without help from individuals or charities. Recently, Tate Britain and Tate Modern announced that their coffers were empty and appealed to artists to donate art. More than 20, including Damien Hirst, David Hockney, Lucian Freud, and Howard Hodgkin, gave pieces.

A National Gallery spokesman said: “Without David Koch we wouldn’t have these remarkable paintings. We are very grateful for his generous help.”

“Calme” and “Tempete” went on show at the gallery yesterday and will remain in London until next summer before they are shipped to America.