Pulling into shore was a small boat full of pale-skinned blokes in odd apparel, yabbering indecipherably and gesticulating with straight sticks.

Advancing with their spears held up, Cooman and his pal were shot at and Cooman, a Gweagal warrior, was wounded.

The date was April 29, 1770, and it was the first landing of Captain Cook and his crew at the future city of Sydney.

“I sometimes tell people Captain Cook’s crew shot my ancestor,” Kelly says.

“But it’s often passed off as just talk. People that don’t know the history think I’m pulling their leg.”

Kelly, a 10th-generation descendant of Cooman, grew up with the stories about how one of Lieutenant James Cook’s landing party shot and wounded his maternal ancestor. So when a Gweagal shield was displayed in Canberra in 2016, he claimed it for his people.

The drab, 1m long by 45cm wide concave bark shield, fashioned from Australian red mangrove more than 248 years ago, was in the inventory of the British Museum. And the dispute has now rewritten history — at least for now.

Kelly, 40, who lives in Bermagui on the NSW South Coast, has visited the British Museum four times in two years in a campaign to have the shield returned to Australia.

He had hoped to return in time to press his claim during British celebrations for the 250th anniversary of Cook’s departure from Plymouth on August 25.

Kelly says his claims to the shield, which he says Cooman used in the first Aboriginal confrontation with Europeans, are supported by members of his mother’s Timbery family, still living around La Perouse.

But he was astonished last month when Australian researchers disputed the shield’s origins, claiming there was no evidence it once belonged to Cooman.

“They also went to my family history and tried to say I cannot prove anything,” he says. “Then they moved on from that to say it is not the shield used by Gweagal men when Cook arrived at Botany Bay.”

Although the mystery is unlikely to be proven one way or another, since Kelly joined calls in April 2016 for the return of Aboriginal artefacts held in European collections, one British and two Australian researchers have contradicted the shield’s provenance, as detailed for decades by the British Museum.

When the shield arrived in Australia for the Encounters exhibition at the Australian National Museum in 2016, director Mathew Trinca repeated the British Museum description. He explained the “remarkable wooden shield” of the Gweagal people was taken by Cook in 1770-71.

“The shield was collected in the aftermath of that fateful first encounter between Cook’s landing party and two warriors on Gweagal land, the beach at a place we now know as Botany Bay, in April of 1770,” Trinca explained.

“The historian Maria Nugent has written extensively of this moment, based on accounts by Cook, by Joseph Banks and other members of the landing party.

In his journal, Cook wrote that two men came onto the beach and challenged his crew as the boats from the Endeavour reached the shore.

“The accounts suggest the landing party fired a warning shot at the two men, but then when they continued to advance, they fired directly at them. One man was wounded and ran off to get a shield. On his return, the party from the Endeavour fired on both men again.”

Kelly,arrived in Canberra in April 2016 to call for the shield, and Gweagal spears held at Cambridge University, to be returned to Australia within three months.

“We are the living bloodline descendants of the Gweagal clan of the Dharawal tribe (and) are at law the rightful owners of all artefacts produced or in possession of our ancestors or found on Gweagal territory,” he says.

“We do claim all artefacts belonging to us and mandate that they be returned to our possession.”

Kelly traces his ancestry to Cooman through his great-great grandmother, explaining he has baptism records linking her to Cooman’s grandson, also called Cooman.

The provenance explained with the shield display in the Enlightenment room of the British Museum states: “Bark Shield from Botany Bay, c.1770. Courtesy British Museum Collection.”

The object description stated: “This bark shield was collected in 1770 on Captain Cook’s First Voyage in HMS Endeavour (1768-71). It is the only indigenous Australian artefact in the British Museum that has been provenanced to the voyages. It is made from wood and bark. Dimensions: 1000mm long X 450mm wide.”

On the British Museum website, item 89 is described as “Australian bark shield”, and continues: “Shield made of bark from Botany Bay, Australia collected in 1770 on Captain Cook’s First Voyage.

“This bark shield was carried by one of two indigenous Australian men who faced Captain Cook and his crew members when they first landed at Botany Bay, near Sydney on the 29 April 1770. After attempts to communicate with the men failed, Cook’s crew fired warning shots.

“This shield was dropped when the indigenous Australians fled. The hole in the centre of the shield was probably made by a wooden spear and there are also traces of white clay decoration on the surface.”

This year Nugent, a historian at the Australian National University, and Gaye Sculthorpe, curator of the Encounters exhibition, backed research by Cambridge University Museum of Archaeology and Anthropology curator Nicholas Thomas that challenged assumptions the shield was collected by Cook’s 1770 expedition.

In two articles published in the Australian Historical Studies titled A Case Of Identity: The Artefacts Of The 1770 Kamay (Botany Bay) Encounter, by Thomas, and A Shield Loaded With History: Encounters, Objects And Exhibitions, by Nugent and Sculthorpe, the authors argue the British Museum shield does not match a sketch of artefacts collected by botanist Joseph Banks during Cook’s voyage.

They also suggest the shield may not have been taken from Botany Bay as it is made from red mangroves native to northern NSW, which do not grow as far south as Botany Bay. But the researchers accept Gweagal people may have acquired the shield in trade with northerly Aboriginal groups.

Sculthorpe, descended from Palawa people in northeast Tasmania, developed the Bunjilaka gallery at Museum Victoria before working with the Native Title Tribunal for a decade.

She was recruited to the British Museum in 2013 to oversee the Oceania section of the museum’s Department of Africa, Oceania and the Americas, sometimes also known as “the rest of the world”.

The section is headed by Australian Lissant Bolton, who worked in the Australian Museum Anthropology division, and 1979 surveyed Australian Pacific collections.

Sculthorpe and Nugent had previously been associated with documents explaining the contested shield was collected by Cook’s expedition in 1770.

Kelly still believes the shield was taken from his ancestor 248 years ago, and says disputes about the shield’s provenance are irrelevant to its return to Australia, preferably to the Australian Museum in Sydney.

But he says staff at Australian museums are not supportive of his attempts to bring home Aboriginal artefacts held overseas. Kelly’s wish list includes five spears, including four displayed at Cambridge University and one in Stockholm, and another shield displayed in Berlin.

“The response from the government and museums has been bizarre,” he says. “These are our national treasures and part of everybody’s history.”

An Australian Museum spokeswoman said it was “open to assisting the shield’s return to Australia but wants to be guided by the Aboriginal community from which it belongs and at their request within the law”.

After sitting at the British Museum display for two days, and spending two hours watching visitors to the Cambridge University, Kelly says the Australian artefacts are largely overlooked by visitors in the mass of items on display in England.

“When I see the artefacts, I’m very proud to do something for my ancestors who haven’t got a voice,” he says. “My mind often goes back and thinks of that first contact and what my ancestors were thinking at that point.”