London — Descendants of some of Britain's wealthiest slaveowners are calling on the U.K. government to publicly apologize and atone for the country's historical links to slavery. Several British families are leading the campaign as part of a group called "The Heirs of Slavery," which is working to shine a light on this country's deep involvement in the slave trade.

One of the group's founders is a second cousin of King Charles III, but the royal family itself — the monarch's own siblings and offspring — are not directly involved in the effort.

CBS News met the Earl of Harewood, the British aristocrat who is the king's second cousin, at his ancestral home, Harewood House. The palatial estate, now open to the public for tours, was built entirely on the profits of the transatlantic slave trade.

"I'm ashamed that, you know, people behaved in that way, that my ancestors behaved in that way," Harewood told CBS News. "We're accountable for that legacy today."

Harewood House is full of art that depicts the earl's aristocratic forebears who grew rich by owning sugar plantations in Jamaica and Barbados that exploited the labor of trafficked Africans.

When Britain finally outlawed slavery in its colonies in 1834, like other slave owners, Harewood's ancestors were compensated by the U.K. government, to the tune of around $3 million in today's money.

"The slaves who were freed received nothing," Harewood noted.  

He has helped to launch the campaign calling for families like his own, that benefited from slavery, to come clean and use their wealth to benefit the descendants of those who were trafficked. He calls it reparative justice.

"It's something that people have been very much in denial about — swept it under the carpet, pretended it hadn't happened," he told CBS News. He said he couldn't fully understand the denial by other families, but assumed it likely stems from a sense of guilt or shame.

Joe Williams is a descendent of British-owned slaves in Jamaica who now leads historical tours exposing how the U.K. profited from slavery. He told CBS News that while it would be impossible for contemporary Britons to truly compensate for the "dehumanization" inflicted on Africans stolen from their homeland hundreds of years ago, it was important for the descendants of both slaves and slaveowners and traders to "work together toward doing what we can."

British slave traders trafficked nearly 3.5 million Africans to the Americas, but Williams said many Brits today think and talk about slavery as something that happened in America, not the U.K.

"I can say, hand on heart, that there are legacies of the transatlantic trade which hold me and many people back from being seen as — in some cases — as human beings," he said. The problem, he believes, is rooted in education, or a lack thereof.

Britain's royal family undoubtedly has historical links to slavery itself. Historians say it's impossible to calculate exactly how much wealth the monarchy generated from human trafficking, but some previous kings and queens were directly involved.

Buckingham Palace announced only this month that it was cooperating with an independent investigation into the monarchy's connections to slavery. King Charles and his son and heir Prince William have both expressed sadness about those links, including William telling people on a visit to Jamaica last year that, "the appalling atrocity of slavery forever stains our history."

"I want to express my profound sorrow," said the prince. But he, and all other senior members of the family, have always stopped short of an actual apology.

The official visit to Jamaica by William and his wife Katherine, Princess of Wales, drew demonstrations by people demanding not only an apology, but reparations. The trip was marred not only by the protests, but by images of the royal couple greeting well-wishers through a chain-link fence, which critics said looked like a throwback to the days of colonialism.

The Earl of Harewood is a great-grandson of King George V, who reigned over Britain until his death in 1936, and a second cousin of King Charles III, who is set to be formally crowned in just a couple weeks.

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CBS News asked Harewood if he believed his relatives in Buckingham Place should be leading the charge to acknowledge and take full ownership of their collective past.

"You can never do enough," he said, "and it's not something that's ever going to go away."

Joe Williams said if he could speak with King Charles, he'd make the point that Britain, and its royal family, were already off to a late start almost two centuries after slavery was banned across the kingdom's vast, formal empire.

"So, I think we need some spearheading to get us ahead of where we should be, rather than behind," he told CBS News.

Williams and the Earl of Harewood have already worked together on projects to educate the British public about the country's historical involvement in slavery.

And in the ornate halls of Harewood House, the earl has started adding to his impressive art collection, commissioning new portraits of black British community leaders to hang beside his ancestors.

In:
• King Charles III
• British Royal Family
• slavery
• Britain
• Reparations
• United Kingdom