One of the most beautiful and infamous treasure hoards of the 20th century, 14 pieces of Roman-era silver of staggering quality, will resurface today on display in London, to the consternation of leading archaeologists who regard it as archaeological loot.

Although Bonhams auction house, which will display the Sevso Hoard, insists no sale is planned, the Marquess of Northampton who bought the silver for an undisclosed sum in the 1980s recently said he "hopes" the silver will be sold, and that it has "cursed" his family. It now belongs to a trust he founded.

But the Hungarian government has written to Bonhams to protest at the exhibition and reiterate its claim that the silver was found on Hungarian soil and illegally exported from the country.

Lord Renfrew, retired professor of archaeology at Cambridge, an expert on illicit antiquities, said: "It looks very much as if it is being touted about again. Whether anyone can actually prove it, it is pretty sure that it was looted, and as such it ranks as tainted goods. This is very distasteful."

The Sevso Treasure, with a notional value of more than £100m, had probably already passed through the hands of several dealers before it came to London in the early 1980s, and was bought by the marquess on the advice of the late Peter Wilson, a former deputy chairman of the auction firm Sotheby's.

It is believed by many archaeologists to have been illicitly excavated in Hungary and smuggled out of the country in the late 1970s, and to have cost the life of at least one man. It was last seen in public in 1990, when a planned Sotheby's auction was abandoned after Hungary, Yugoslavia and Lebanon all claimed but failed to prove ownership through the US courts, which found that the marquess was the legal owner.

The marquess, whose estates include more than 30,000 acres and magnificent stately homes in Oxfordshire and Warwickshire, sued his legal advisers after the Sotheby's auction was abandoned, and received a substantial but undisclosed settlement out of court.

The 14 pieces of fabulous silver include four enormous platters, the size of bin lids, each containing up to a stone of pure silver. They may have been made in a Greek workshop for a staggeringly wealthy Roman client, possibly the Sevso who gave the hoard its name in the inscription: "May these, O Sevso, yours for many ages be, small vessels fit to serve your offspring worthily."

The Hungarians believe the silver was found in the late 1970s by Jozsef Sumegh, then a 22-year-old quarryman. He was found hanged in 1980. He is believed to have first hidden the pieces, then sold them on the black market. His death was first explained as suicide, but the Hungarian authorities now believe he was murdered - possibly to extinguish the origins of the silver.

Bonhams will show the silver at private viewings in London. The glossy invitations, sent to collectors, academics and archaeologists, describe it as "the finest surviving collection of ancient silver known to exist".

A spokesman for Bonhams said: "We think it's an astonishing collection, obviously, and we're very flattered to be asked to show it. There is enormous academic interest in this silver, but it has been locked in a vault for the last 16 years. It seems better to us to put it on display than to have it locked away, and we are thrilled and privileged to be given the opportunity to do that."

Roger Bland, a former coins expert at the British Museum, head of the portable antiquities scheme for recording archaeological finds, was astounded when his invitation arrived. "It is very difficult to see what Bonhams hope to achieve through this private viewing. Under [government] guidelines for museums no UK museum could ever acquire or even borrow it. I think the circumstantial evidence points strongly to its having come from Hungary, and I hope that it goes back there and is put on show for public benefit."

The pieces resemble those found near Lake Balaton in the 19th century, now in the national museum in Budapest, and one is engraved Pelso, the Roman name for the lake.

In Budapest Eva Hajdu, responsible for the Sevso case within the ministry of culture, said negotiations with the marquess broke down some years ago.

She said the Hungarian government believes it could win a legal claim. But no such claim has yet been lodged.

"We would like to announce to Bonhams, and to the art world, that this is Hungarian property," Ms Hajdu said.

Retired detective sergeant Richard Ellis, formerly of the art and antiquities squad at Scotland Yard, who for years tried to track the provenance of the silver, said: "Am I 100% certain of what happened with it? No. Let's say that the evidence stacks up, and that there is a total lack of evidence on the other side. And from what I have seen of the evidence, I do not believe that that man committed suicide."

Backstory

The Sevso Treasure, 14 massive Roman era silver bowls, salvers and ewers, believed to date from between 350AD and 450AD, was brought to London in the early 1980s with an export licence from Lebanon, later claimed to be a forgery. The Hungarian government, backed by many experts, is convinced the hoard was found in their country in 1978 by a quarry worker, and illegally exported. The silver was bought as an investment by the Marquess of Northampton, on the advice of the late Peter Wilson, former chairman of Sotheby's. In 1990, when a Sotheby's auction was announced and the silver was on display in New York, Lebanon, Hungary and Yugoslavia all lodged legal claims to it. In 1993 the American court found that none could prove title, and that the marquess was the legal owner - but the silver, left without any agreed provenance, has been regarded as unsaleable.