It was one of the most shocking chapters in Britain’s long, bloody subjugation of Ireland: the buying, selling and transportation of Irish chattel slaves to the colonies in America.

Manacled and brutalised, they filled the bellies of ships that crossed the Atlantic and were put to work on plantations in the Caribbean and North America, sweating till they died in service of empire and profits.

The historical focus on slaves from Africa overlooked Irish slaves until recent years when rediscovery of their existence lit up corners of the internet and became a meme.

The only problem: it was not true. Irish migrants experienced indentured servitude, a form of bonded labour, but not perpetual slavery based on race. The notion of Irish slaves is disinformation spread online by white supremacists, mostly outside Ireland, to puncture black people’s anger over slavery.

“Those who propagate the myth tend to live in former white settler colonies like Australia and the US and seek to undermine movements like Black Lives Matter,” said Ciaran O’Neill, a history professor at Trinity College Dublin. “They want to create false equivalence between the Atlantic slave trade and the phenomenon of indentured Irish labour in the Caribbean.”

In reality some high-profile Irish people bought, owned and trafficked African slaves – a collusion in empire that Ireland has preferred to overlook.

This historical chapter is now being rediscovered. Trinity College Dublin, founded in 1592, has launched a two-year investigation into its colonial past that will scrutinise funding, curriculums and scholars, including George Berkeley, a slave-owning philosopher after whom Trinity’s library was named.