To my distant cousin Justin Welby: our family’s slavery history is truly awful. Let’s be open about it | Alex Renton

I don’t know my newfound cousin Justin Welby, the archbishop of Canterbury. We’re not close, in any sense. But we do have a mutual great-great-great-grandfather: Sir James Fergusson of Kilkerran, who died in 1838. He is five generations back on Welby’s side, six on mine. It is not as wildly unlikely as you may think – at six removes we all have 128 grandparents. But this particular historical figure is significant because of what he and tens of thousands of British people like him did – the fallout of which is still dividing and toxifying society today.

Welby’s statement confessing Fergusson’s slave-owning past shows he may not know much about our shared forefathers. So here is some detail. Fergusson and the generation before him were owners of enslaved Black people in Jamaica and, for a while, Tobago. There were 160 to 200 people at any one time at the Jamaican sugar plantation Rozelle, with 75 at Bloody Bay in Tobago.

It was an ongoing massacre. In the worst years, more than 20% of the adults died, mostly from disease and violence; infant deaths were so common they were not recorded. Before 1807, the year shipping humans from Africa was abolished, Caribbean planters found it was more economically beneficial to work a person to death rather than look after them. The British transported 3.1 million Africans across the Atlantic – when slavery was abolished, after 250 years, there were 800,000 enslaved people remaining.

The Fergussons were quite ordinary, small-scale enslavers – far less significant in wealth than the bankers and insurers. What our ancestors did was legal, of course, actively encouraged by British governments for the considerable tax revenues. Fergusson’s uncle, Sir Adam Fergusson, sat as an MP, voting for the navy and army to protect his West Indies interests, just as he voted against William Wilberforce’s attempts to abolish the “slave trade” in the 1790s. Sir Adam and his brother dabbled in shipping kidnapped people from modern Ghana to the Caribbean themselves.

When it was clear that trade would eventually be banned, Sir Adam encouraged his managers to buy more young women so he could breed new workers, just as you breed farm animals. That failed. The teenagers died or failed to produce nearly as many children as he had hoped. He became very cross (I have read his letters to his managers at the plantation in Tobago).

But the most important point I would make to cousin Justin is that this was entirely racist. Our Christian ancestors could not legally or morally have enslaved a white person. For their consciences, they had to make Black people not human at all. All the enslaved people had their African names erased and replaced with the sort you might attach to a pet dog. They rejected moves to baptise or educate them – that would be to acknowledge their humanity. In Tobago, the Fergussons branded their “property” with a logo made of their entwined initials.

Welby has not held back on the church’s complicity. The Church of England committed a “vile and disgusting sin”, he said in a sermon in Jamaica in July, not just in the moral support it gave the enslavers but in profiting itself. Some archbishops did so directly. Welby said: “We are deeply, deeply, deeply sorry.”

Over 250 years, many enslavers put a slice of their wealth into the church’s collection plate. Were they seeking atonement? Welby has pushed for those donations to be acknowledged and for the soon-to-be-launched Church Commissioners’ reparative justice fund – all in a storm of vicious criticism from the right wing in the church. “Woke Welby” and even “anti-Christian” are some of the insults thrown at him. The abuse from Telegraph-reading Anglicans hurts him more than it should, but it is the establishment into which he was born and educated.

But Welby has admitted his connections. And now he must go further. Apology and acknowledgment lead logically to support for calls for reparations, in the Caribbean, West Africa and here. It’s a progression that many families with this story, from Britain and other enslaving nations of Europe, have embraced.

Last year, some of us set up Heirs of Slavery to encourage others who were ready to acknowledge that their ancestors profited from enslavement to support attempts to heal the still-open wounds. When people come forward, we suggest they research the history fully and listen to those descended from the other side of the story. I have done that with people all over the UK and at the sites of the Caribbean plantations that my ancestors never visited. I am still learning.

Regrettably, there are some who deny the continuing significance of this history. It is a further cruelty – one that Tory leadership candidates have been shamefully indulging in again this week. Meanwhile, the government has dismissed the notion of discussing reparations. It is not on the Commonwealth meeting agenda, despite the fact that most other nations still bothering to turn up do want to talk about post-colonial reconciliation. Labour’s stance is deeply shortsighted, a betrayal of all the people who still have some faith in British morality and justice. Welby could say so.

His story shows how deeply embedded this past is in us. More than 2 million Britons are as connected as myself and Welby to those who received the compensation money paid out to slave owners by the British government in 1833 after the abolition of slavery. Many more are connected to the wealth generated by all the slavery-dependent industries, from banking and insurance to shipbuilding and the weaving of cloth for enslaved people to wear.

The man the archbishop crowned last year is the most significant heir of slavery of all; the connections run through every antecedent from Charles II to George IV. Welby can now help the king, the head of the Church of England, to speak the truth about his ancestors. For Welby to convince such a totemic public figure to deliver the apology so long called for would leave a lasting legacy – and truly start the process of reconciliation.

• Do you have an opinion on the issues raised in this article? If you would like to submit a response of up to 300 words by email to be considered for publication in our letters section, please click here.