Derek is a member of Slobsters gang the 'Bad Dudes'  and the absolutely worst person you will ever meet. He is rude, foul mouthed, racist and very against paying his taxes. Even the Doctor after exchanging a few short sentences with him was rendered dumbstruck by how awful he was.

As the worst person in Cumberland he was replaced by the second most Radical Man in the Radical land, Ron Wizard. The 'Most' Radical man, King Radical being in Cumberland already