A 13th Century masterpiece which for years hung unnoticed on a landing in a country house has been described as a "once in a lifetime find" by art experts.

The painting of the Madonna and Child enthroned with angel, by Italian master Cimabue, was discovered by Richard Charlton-Jones of Sotheby's.

The Old Masters expert had been cataloguing the works for a house sale at Benacre Hall, near Lowestoft in Suffolk. They are being sold as part of the estate of Sir John Gooch, the 12th baronet of the property, who died in April last year.

Despite measuring just 10 inches by eight, the gold ground panel is expected to raise �2m at auction, Mr Charlton-Jones said.

Staff at the hall had no idea of the painting's significance or value.

But Mr Charlton-Jones said the discovery was so rare it would probably never be repeated.

He said: "I had trembling knees when I first realised what it was.

"It wasn't until much later that it really began to sink in.

"It is extremely rare. There has never been one like this on the market, anywhere, ever."

The work, depicting the Madonna and Child s, was thought to be potentially of great importance and was brought to the National Gallery in London for study.

It was then transferred to New York, where it was finally confirmed as a Cimabue.

Cenni di Pepo, called Cimabue (circa 1240-1302), was the most important figure in the development of Italian painting in the late 13th Century and is a seminal figure in the history of Western art, Sotheby's said.

'Rarity and beauty'

It will be the first time one of his works has been offered at auction.

Mr Charlton-Jones said: "This painting is one of only seven or eight independent panel paintings by Cimabue that survive and the only known one in private hands.

"It is a picture of the very greatest rarity and beauty, and a discovery of enormous significance."

The picture is thought to have been acquired by Edward Sherlock Gooch 6th Bt of Benacre in the early 19th Century.

It is expected to be auctioned at Sotheby's in July.