Slavery was never lawful in England, though it existed. Obviously it was allowed in the colonies. (Before anyone bites my head off, yes England did benefit massively from the trade, and its legacy persists in eg placenames in Bristol etc - I’m just answering parent’s query)
There was substantial indentured labour and serfdom in England too. Surely simple redistributive tax based on wealth is fairer?
Anyway how do you determine whos ancestors had slaves, or weren’t involved, or were slaves? You want to start tracing bloodlines?! Should the English pay the Irish?
England’s really not violent at all.
There were multi-generation serfs and indentured labour in the British isles. There were also slaves taken from the isles, though a very long time before then.