Modern slavery is still most prevalent in Africa, as it was before whites colonised it, as seen in this map of modern slavery on Wikipedia.

Britain has been free of legal slavery for over 200 years, and Europe for 150.
However, due to mass immigration over the last twenty-three years since the Blair government opened Britain up, there has been a massive increase in illegal modern slavery.
Moreover, a lot of that has been of white British people, groomed into slavery due to their neglect and poverty by their own government!