The descendant of an Indigenous Australian warrior who was the first to confront Captain Cook as he landed on the shores of Australia in 1770 has demanded that the British Museum give back a shield “stolen” by the English invaders.

Rodney Kelly, the sixth-time great grandson of warrior Cooman who stood his ground as Cook’s HMS Endeavour landed at Botany Bay more than 200 years ago, has made a formal claim for the repatriation of the Gweagal Shield that once belonged to his ancestor.

Cook’s diaries, and sketches made by the crew, recount the events of April 1770 when they approached the coast of Australia and encountered two warriors raising spears to defend their land. In response, the English voyagers fired off their muskets, hitting warrior Cooman fatally in the leg. The tribesmen ran off, leaving behind their spears and shields, which were picked up by Cook’s crew, brought back to the UK and have been in the British Museum’s collection ever since.

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However, Kelly believes that the time has come for the return of the shield, which is of “utmost significance” to Indigenous Australians when “my people are suffering and our culture is dying”.

Kelly travelled with a delegation to meet the British Museum deputy director, Jonathan Williams, to discuss the return of the shield and issued a formal statement to the museum’s trustees for its repatriation.

“The Gweagal Shield is a gateway that has the potential to open the discourse on the tragic modern history of the Indigenous Australians under colonisation,” said the letter, which was signed on behalf of the Gweagal elders, ancestors and people. “The British Museum must realise that this sacred object still has vital and imperative cultural work to do in Australia. The healing power that this shield has for Australia is much greater than any value it can have as part of a collection in the British Museum.”

The museum in central London owns about 6,000 Indigenous Australian items variously acquired after British contact, invasion and occupation of the continent beginning in 1770, but the Gweagal Shield is considered the most important.

Kelly said the museum was “not receptive” to returning the shield at their first meeting but had offered to open discussions about a loan. One of the offers was that the shield could be lent for three years, with the possibility of an extension.

A British Museum spokesperson said: “Some objects, such as the shield, are of high cultural significance for contemporary Indigenous Australians. At the meeting, we discussed how the museum is open to discuss lending the shield, subject to all our normal loan considerations.”

The museum said the shield was available to study online, adding: “We believe that the museum is a unique resource for the world … The shield is a vital element in this interconnected world collection and serves to inform a world-wide public of the long-standing cultural significance of Indigenous Australian communities.”

However, Kelly said that was not enough and he would continue to fight for the shield’s permanent return to Sydney, where it could “help right the wrongs of history and how our people’s history is told in Australia”.

He said that for Indigenous Australians looking for connection to their past, and a sense of identity, the shield was “where it all began”.

Kelly is also pursuing the repatriation of several of the spearsthat now sit in the collection of the Cambridge Museum of Archeology and Anthropology. The museum confirmed it had received a formal request for repatriation and its director, Prof Nicholas Thomas, said it would be considered “very carefully, and with an open mind”.

Kelly said: “That shield and those spears represents how Australia was conquered, not discovered and the genocide of our people that took place from that moment onwards. This is where it all started for us, where our right to life and land and culture was denied, and the world needs to know that.

“In history, we are just the savages. People in Australia are taught that Cook just walked on to the shore that day, found an abandoned camp where he peacefully exchanged some spears and shields with some beads. But these artefacts can teach a new generation how it wasn’t peacefully settled, that from day one we were shot at. Rewriting our history is a big part of what has motivated me with this fight.”

A motion has been passed through the New South Wales parliament which formally acknowledges that the Gweagal people are the “rightful owners” of the shield and spears and that the hostilities enacted upon the aboriginal warriors on that day in 1770 were “the first act of a genocide of the indigenous population known as the Frontier Wars”.

Kelly said that if permanent repatriation negotiations failed, he would launch a legal battle for the return of the valued artefact.

Kelly described the experience of visiting the shield at the British Museum, where it is displayed alongside other Polynesian artefacts, as “really sad and disrespectful”.

He said: “Back home, it could do so many things for me and my people, but in that case in the British Museum, it’s as if it means nothing.”