It is hard to imagine why somebody at the Treasury thought that the subject of slavery was fertile territory from which they might harvest their weekly “surprising #FridayFact”. Just after lunchtime on 9 February the department’s Twitter page presented its third of a million followers with its latest offering. “Millions of you helped end the slave trade through your taxes,” it trumpeted.

Below, under an image of Africans being marched, in yokes and ropes, into slavery, the tweet continued: “Did you know? In 1833, Britain used £20 million, 40% of its national budget, to buy freedom for all slaves in the Empire. The amount of money borrowed for the Slavery Abolition Act was so large that it wasn’t paid off until 2015. Which means that living British citizens helped pay to end the slave trade.”

The “fact” had the unctuous feel of a pat on the back. A little over a week after millions had been given their self-assessment tax bills, the good people at the Treasury threw us something to cheer us up. You might be skint, you might want to weep when you see your bank balance but look, you helped to end slavery, at least it’s all for a good cause, eh?

What the Treasury didn’t mention, though, was that the £20m was paid out to the 46,000 slave owners, to compensate them for the loss of their human property. By one calculation that is the modern equivalent of about £17bn. Is this really something we should regard with collective pride?

Few people in the 1830s would have seen it that way. Compensation was a mechanism by which Britain was finally able to end a system that millions of people had come to regard as abhorrent, and a national disgrace. It was a way out. The abolitionists agonised over it. To accept the principle of compensation was at odds with their fundamental moral position: that it was impossible for one human being to own another, to hold “property in men”, as they put it. The only people who saw the payment of compensation as a positive were the people who had spent three decades campaigning for it and would be the beneficiaries of it – the slave owners. ...