We've already paid to end slavery - no good can come of trillion-pound reparations

So-called "decolonisation" is threatening to become expensive. Last month the African Union joined the Caribbean Community in demanding reparations from the UK for "colonial crimes" - especially slavery. Caricom has already submitted a bill of £18trillion and the African continent's claim is likely to be even higher.

Such decolonisation is already expensive for the Church of England, whose leadership has decided to spend an initial £100million on slavery-reparations after research apparently revealed that the Queen Anne's Bounty, an 18th-century fund supporting poorer clergy, had "links" with African enslavement through investment in the South Sea Company

The church, it seemed, had made itself part of the "multinational white establishment that deprived tens of millions of Africans of life and liberty". Except that it didn't, for the researchers had misunderstood the data. The Queen Anne's Bounty didn't invest in the company's slave-trading operations at all. And those who did made no profit from them since they were consistently loss-making.

What's more, the tale of a 'white establishment' exploiting innocent African victims is a divisively racist caricature of the truth. The 'black establishment' was even more to blame. Africans had been enslaving other Africans for centuries.

Those they didn't consume in human sacrifices, they sold first to the Romans and then to the Arabs. A few years before the first British slave-ship arrived on the West African coast in 1563, a Portuguese witness had reported that the African kingdom of Kongo was exporting overseas between 4,000 and 8,000 "pieces" [slaves] annually.

Three hundred years later, Fulani Africans were running vast slave-plantations in the Sokoto Caliphate in what's now northern Nigeria, exploiting the same number of slaves - some four million - as in the whole of the United States.

Meanwhile, unlike Africans, the British had repented of their involvement in slave-trading and slavery, and in the early 1800s were among the first peoples in the history of the world to abolish them. They then used their imperial dominance to suppress them from the Pacific North-West, across India, to Africa. In mid-century, the Royal Navy devoted more than 13% of its total manpower to stopping slave-traffic between West Africa and Brazil.

At the same time, Sir Thomas Fowell Buxton's idea that the key to ending the slave trade and slavery in Africa was to promote alternative, 'legitimate' commerce, was gaining traction. This led to the setting up of trading posts in West Africa, and then, when the merchants complained of the lack of security, a more assertive colonial presence on land.

In 1851, having tried in vain to persuade its ruler to terminate the commerce in slaves, the British attacked Lagos and destroyed its slaving facilities. The sustained British commitment to stamp out slavery was expensive in both blood and treasure. Seventeen hundred sailors died in the service of the Royal Navy's campaign to stop maritime slave-trading. Meanwhile, on land, Christian missionaries risked - and often spent - their lives striving to shut down slave-markets in Africa.

Among them was the Anglican bishop John Mackenzie who died horribly of blackwater fever in what is now Mozambique in 1862 at the age of 37.

What did all this cost in pounds and pence? David Eltis - described by the African American historian, Henry Louis Gates of Harvard University, as "the world's leading scholar of the slave trade" - has estimated that the campaign to suppress transatlantic slavery alone cost British taxpayers more than the total of eighteenth-century profits. Political scientists Chaim Kaufmann and Robert Pape have described that campaign as "the most expensive example [of costly international moral action] recorded in modern history".

Propelled by 'progressive' zeal, the Church of England's leaders have made a serious mistake. For the last 18 months, a leading Anglican ethical expert, two Oxbridge historians, a retired Old Bailey judge, and a descendant of African slaves have been trying to persuade them to rethink. Yet, apart from one shoddy online response, those responsible have arrogantly offered no defence of their policy.

Instead, they have defamed their critics as liars, deliberately spreading falsehoods. They've evaded criticisms by declaring that they won't respond to arguments that African descendants find 'offensive' (even if it's the truth that offends). And they've issued veiled and intimidating threats of legal action.

This issue is not going to go away. Questions are now being asked in Parliament. If the Church's leaders keep on digging a deeper hole - and in such an unscrupulous fashion - they risk a major national scandal. Reputations may not survive it.

• Lord Biggar of Castle Douglas CBE is the author of Reparations: Slavery and the Tyranny of Imaginary Guilt