“The fact is, my ancestors bought girl slaves so they could give birth to more slaves,” Renton told South China Morning Post.

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“This system was legally encouraged by the Crown and was entirely racist,” said Renton, who was educated at Eton, the same elite school as Prince William, King Charles’ oldest son. “As a group, we think the royal family aren’t really different from hundreds and thousands of others, because a lot of their wealth came from the industrial complex of slavery.

“On top of that, he is the richest royal in Europe and has a personal fortune estimated to be worth £1.8 billion (US$2.2 billion). He has something to acknowledge, and could do a lot of good.”

Britain’s involvement in the slave trade started in 1562. In 1663, King Charles II granted a charter to the Royal African Company, giving it a monopoly over the slave trade in West Africa.

By 1730, Britain was the world’s top slave-trading nation. The British shipped about 3.1 million African men, women and children to the Caribbean, Americas and elsewhere, where they toiled on plantations.

Slavery was abolished across the British Empire in 1834. Britain’s government approved £20 million to compensate slave owners for their loss of “property”.

That hefty amount – equivalent to about 40 per cent of the government’s annual budget at the time – was finally settled by British taxpayers in 2015.

“Anyone who had any wealth in the 19th century in Britain had links to slavery in some way … and you cannot disentangle that from cruelty,” Renton said.

Others with Heirs of Slavery include former BBC television journalist Laura Trevelyan, David Lascelles, the Earl of Harewood who is a second cousin of King Charles, and businessman Charles Gladstone, a direct descendant of former prime minister William Gladstone whose family fortune came from slavery.

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Slavery remains a bitter reminder in nations that are, or until recently were considered realms of the UK monarchy.

Ralph Gonsalves, the prime minister of St Vincent and the Grenadines, said last week it was “absurd” that King Charles was still head of state of former colonies thousands of kilometres away from the British mainland.

King Charles has shown willingness to deviate from a common narrative that has emphasised how Britain was at the forefront of slavery abolition. He has also called for more research into the royal family’s role in the slave trade.

“From the darkest days of our past, and the appalling atrocity of slavery, which forever stains our history, the people of this island forged their path with extraordinary fortitude,” King Charles said during a 2021 during a visit to the former slave colony of Barbados, to mark the transition of the Caribbean island to a republic.

Last year, Prince William expressed “profound sorrow” for slavery during a visit to Jamaica where he faced protests.

According to the United Nations special rapporteur on the promotion of truth, justice, reparation and guarantees, a proper apology entails “acknowledgement of the facts and acceptance of responsibility for the harm inflicted and constitute a form of reparation under international law”.

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Last month, Portugal’s President Marcelo Rebelo de Sousa said his country should apologise for its role. It was the first time a leader of Portugal had publicly suggested such a national apology.

Also last month, French President Emmanuel Macron paid homage to Toussaint L’Ouverture, a key Haitian figure in the 1791-1804 Haitian Revolution, which is considered the only successful slave revolt in history. Following the revolt, Haiti then abolished slavery and was granted independence from France its colonial ruler.

Macron did not apologise for France’s role in the slave trade, nor mentioned the 1825 French indemnity demand that forced Haiti pay it 30 million francs in compensation.

That debt, worth around US$30 billion today, is seen as a major contributor to the country’s crippling poverty.

Sunak last month said “trying to unpick our history is not the right way forward, and it’s not something that we will focus our energies on”.

Grietje Baars, a senior lecturer in law at City, University of London, said that although an official apology from Britain would make the argument for reparations stronger, “the risk exists that this remains solely on the symbolic level and is seen as having ‘done enough’ – with or without some symbolic material reparations”.

“I would say that even without an apology it is pretty obvious who was responsible for the trade in enslaved people, and who has reaped the many benefits from it,” Baars said.

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Renton says per capita reparations were highly unlikely, even if apologies were made.

“The British taxpayer dipping into their pockets and handing out billions will never happen,” he said.

However, he believes Britain owes its former slave colonies development assistance for infrastructure projects, as requested by them.

He points out that the UK has drastically cut the amount of aid it gives to Caribbean nations over recent years, failing the nations “who enriched Britain more than anywhere else”.

He said some countries, like Guyana, are among the poorest nations in the Americas but are “neglected because they are not strategically important to the UK”.