Image caption The auctioneer's website describes the stone as "beautifully carved"

A garden doorstep at a home in Devon in the UK has been identified as a rare Sri Lankan artefact expected to fetch more than £30,000 ($47,500) at auction.

The auctioneer Bonhams says the carved granite step is a Sandakada Pahana - or moonstone - similar to those found in temples dating from Sri Lanka's Anuradhapura period (c400BC-1000AD).

Sri Lanka's director of archaeology says it is unclear if it is authentic.

But if so, he believes the authorities should take steps to acquire it.

The stone was found in the garden of a bungalow in Devon. Its owner said that it was originally in a home in Sussex that her family had bought in 1950.

Bonhams says the house had been purchased from a tea planter who had lived in Sri Lanka.

Experts say that the discovery of such a stone outside of Sri Lanka is extremely rare.

Senerath Dissanayake, head of Sri Lanka's archaeology department, said it could prove very difficult to secure the return of such an item to Sri Lanka because legislation might not be adequate to support such a move.

"It could be in a diplomatic manner by talking to the parties - or by law. But until we verify the authenticity, we cannot think of law," he told BBC Tamil's Jeyapragash Nallusamy.

Dr Dissanayake also said that the department had kept records in the Anuradhapura district since 1890 and he could see no reason why the removal of such a stone would not be recorded.

'Beautifully carved'

The auctioneer's website describes the stone as "beautifully carved" and "featuring a curved procession of animals including lions, horses, elephants, birds and Brahim cows."

Bonhams said it believed the "provenance to be accurate and fulsome and correct and the object is as described".

The stone will be put up for auction in Bonhams' Indian and Islamic sale in London on 23 April.

The original owner of the moonstone was four years old when they moved to Sussex, her husband, Michael Hickmott, told BBC Sinhala. "As a child she would be playing with it in the garden."

They moved the stone with them every time they moved house.

But it weighs almost a tonne and measures 8ft by 4ft. The owners were keen to move to a smaller house and, after meeting with a Bonhams expert, invited him to look at the stone, which was lying at the end of a path in their garden.

"When I saw the photographs and she explained the full story, I knew that it could be of great historical interest and importance," Sam Tuke of Bonhams in Exeter is quoted as saying.