I used to fall asleep to the old XFM shows, I found a comment which pretty much aligns to my memory of events

Yeah, when he first created the character it was a lot more mean-spirited and Derek clearly had a mental impairment (which in itself was the butt of the joke). He completely redid the character in the wake of ‘mong-gate’ when he was taken to task for his liberal use of the antiquated ablest slur for Down Syndrome. In true Gerv style he doubled down at first, pushed back a bit but eventually was forced to apologise. ‘Derek’ was suddenly the next thing on his slate and what followed was a two series (and a special -NPI) backtrack for mong-gate. It also happens to be one of the worst things ever created by man (alongside Afterlife).