During his tour of Jamaica this week, David Cameron dismissed the growing calls for Britain to apologise and pay reparations for the nation’s role in the transatlantic slave trade. He argued that Jamaica needed to “move on” from that horrendous chapter in history, and spoke of Britain’s pride in its role in abolishing the slave trade.

During his campaign against Scottish independence he also invoked the idea of the nation being progressive when he claimed that Britain was a country that was worth saving because, among other things, it “abolished slavery”. For Cameron, it seems, the act of abolition was “British”, but the atrocity of slavery was not.

The progressive myth of Britain’s role in the enslavement of Africans is part of a wider historical delusion. This myth-making was at its most prominent during the 2007 “celebrations” of the bicentenary of the Abolition of the Slave Trade Act. Much was made of the anniversary, regardless of the truth that the act only applied to the trade of Africans to the Americas and in no way ended the practice of slavery (which formally continued in Britain until 1840).

The nation used the anniversary to promote this progressive myth, almost deifying the abolition campaigner William Wilberforce and his heroic campaign. There was even an accompanying film, Amazing Grace, to memorialise “the great King Wilberforce”, released the year before the anniversary. Toyin Agbetu, who became infamous for disrupting a royal abolition ceremony, dubbed the “celebrations” as a “Wilberfarce” because of the focus on the white saviour.

Not only did this narrative provide Britain with a positive spin on its involvement, it also undermined the role of black agency in bringing about the end of the slave trade. It is no coincidence that the trade in Africans was abolished three years after the Haitian revolution.

One of the causes of the revolution was that a large percentage of the enslaved in the colony had been born in Africa. Western powers were terrified of the prospect of further rebellions, and this is a key reason why the trade was abolished, but the practice continued. The enslavement of Africans ended for a number of reasons, mostly economic concerns, and pragmatic responses to rebellion.

Even if Britain had had a moral awakening and stopped the atrocities, there should be no praise. If you commit a crime for centuries, then realise it was immoral, it would be absurd to celebrate your achievement. You would still be arrested, punished and made to face the consequences. It is for precisely this reason that the progressive myth is so entrenched and important to Britain.

If you commit a crime for centuries, then realise it was immoral, it would be absurd to celebrate your achievement

Britain was built on the basis of slavery and colonialism. Without the “empire where the sun never set”, the nation would not exist in anything like the same form today. In terms of the enslavement of Africans, conservative estimates are that between 10% and 20% of current GDP can be linked back to exploited and unpaid African labour. At abolition, slave owners received compensation, while the formerly enslaved received nothing other than an effective return to the slave system under apprenticeship and then colonialism.

The legacies of slavery are clear to see in the poverty in the Caribbean and racial inequalities in Britain. In any rational analysis, it is clear as day that Britain owes a substantial debt to the descendants of those who were enslaved.

The purpose of the progressive delusion is to justify the unjust through appeal to the irrational. It allows Cameron to visit Jamaica with his patronising message of “it’s time to move on”, and to express pride, without properly acknowledging Britain’s role in the kidnap, slaughter, rape and exploitation of millions of Africans. These historical delusions allow him to present Britain building a prison on the island – so that he can deport Jamaican prisoners in Britain back to their country – as an investment in Jamaica’s infrastructure.

The delusions that keep the nation comfortable have what Kwame Nkrumah, the first president of an independent Ghana, called “an Alice in Wonderland craziness about them”. As much as Cameron, and the nation, need to wake up to the realities and legacy of the enslavement of Africans, the truth is they are firmly trapped down the rabbit hole.