Derek is a claimed 'Spiritual Medium' who says he can communicate with the dead. He has appeared regularly on several satellite-TV ghost-hunting type shows in the UK since the late 90s, most memorably on Most Haunted with Yvette Fielding.
At a Most Haunted investigation into an abandoned jail, a producer told Acorah names of inmates who had faced the death sentence. These spirits - named Kreed Kafer and Rik Eedles - were duly 'contacted' by Acorah in the show. He even acted as though these spirits where inhabiting his body.
Unfortunately, these were fake names - anagrams of Derek Faker and Derek lies - made up by the show parapsychologist Dr. Ciarán O'Keeffe.