Historian Sir Roy Strong, author of The Story Of Britain, said: "This stands history on its head, projecting back on to the past something that isn’t true.

"The only Africans who came here were a few with the Romans who came and then left. I find it disturbing that our children should be taught something that is clearly designed to feed into contemporary problems rather than tell our island’s story properly."

Pretty much sums it up. It's more about indoctrination than education.

The influence of indoctrination is very obvious, they even filled the Wiki page on British black population with misinformation:

These communities flourished in port cities strongly involved in the slave trade, such as Liverpool and Bristol. By 1795, Liverpool had 62.5 per cent of the European Slave Trade. As a result, Liverpool is home to Britain's oldest black community, dating at least to the 1730s. Some Black Liverpudlians are able to trace their ancestors in the city back ten generations.