The British were engaged in the slave trade, then worked to outlaw slavery but replaced it with indentured servitude that was basically like slavery with a trivial income. That and exploitative colonial government meant you don't need slavery to loot everything.
Reparations are a different topic and wouldn't necessarily solve the problems of slavery/colonization.
A great many countries were engaged in the slave trade, especially those where the slaves originated.
The British had the comparative advantage in shipping