It all depends on what you mean by the folk scene. If you mean the clubs & sessions where middle class white people go to sing olde Englishe & Scottishe folke songes and play the Irish tune, then you won't find many black people there. (It always seems a shame to me that British folk music prefers to live in a tiny ghetto where it's not heard by the majority of British people, of any colour or culture). If you mean the festivals, you will find a higher proportion (though still small). Many influences from all over - reggae, ska, music from many regions of Africa, Asia and Latin America, blues - are now quite normal. Bands like the late Edward 2, the current Boka Halat, Baka Beyond had/have mixed line-ups. If you simply mean folk music in its broadest sense - in that every country has some - then the big English cities are full of black folk music of one sort or another.