In colour: the Edwardians as we've never seen them before

At a time when most amateur photographers were confined to ghostly monochrome images of family or friends, Lionel De Rothschild had it all. He had money, access, a good eye – and most all he had colour.

A collection of previously-unseen pictures captured by the scion of the banking dynasty at the turn of the 20th century has cast new light on the era with the discovery of the earliest-known colour photograph of King Edward VII.

The photographic talents of Lionel, the head of the NM Rothschild & Sons merchant bank who was hitherto better known for his interest in horticulture, only emerged after his grandson, also called Lionel, found the images in a cupboard at the family's Exbury Estate in Hampshire.

De Rothschild was a pioneer of Autochromes, a new method of taking colour photographs which was first demonstrated by the Lumière brothers in 1903 and put on sale in 1907.

But while allowing photographers to capture colour images with ease for the first time, the technique was way beyond the pocket of most amateurs – reserving it for an elite strata of monied enthusiasts.

De Rothschild began experimenting with the technique in 1908, building up a collection of seven hundred autochromes, including the first colour photograph of London Zoo, each kept wrapped in newspaper to preserve the freshness of the tones.

Victor Gray, coordinator of a forthcoming exhibition of the photographs, said: "For the first time, colour photography was within the remit of an amateur as long as he could afford it. It's hard to explain the quality of the colour and imagine the astonishment when autochromes were first displayed."

But the process had its limitations. After initial enthusiasm, they were abandoned because the plates could not be copied or printed and they had to be viewed through a light viewer. But with the aid of modern technology, the pictures have been able to be scanned for the first time.

De Rothschild's pictures offer a new perspective on the Edwardian period. Lionel De Rothschild, who continues to receive King Edward VII's great-grandaughter at Exbury, said. "We believe this must be one of only a very few colour pictures taken of the King. It would be interesting to find out if it is indeed, the only colour image." The picture, which shows the King dressed in Highland costume, is an informal portrait taken eight months before his death. It was shot 15 miles from Balmoral at Tulchan in Strathspey. De Rothschild, who was keen on shooting, had been on a trip to Scotland for the autumn grouse season. He also took pictures of Lady Helen Vincent, a renowned beauty and wife of diplomat Sir Edgar Vincent. His family life is also depicted, with a picture of his fiancée Marie-Louise Beer in 1912.

Although de Rothschild was a banker, it is not just his photographs that show that the friend of Winston Churchill went against the grain of his family's tradition.

Educated at Harrow and Cambridge, he joined the family business, but he moved to Exbury in 1919 where he became a horticulturalist. The estate gardens, which he planned and planted himself, have since become world famous for the Rothschild Collection of rhododendrons and azaleas. The exhibition, The Colours of Another Age, will be at Exbury from May 1.